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ChrisRoss

Member Since 13 Feb 2016
Offline Last Active Today, 04:06 AM
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#407117 Beginner question: Mininum focusing distance

Posted by ChrisRoss on 13 June 2019 - 11:51 PM

What I find can happen with the contrast detect AF systems is they "look through" the subject to focus on what is behind if it has more contrast than the subject or if the subject is a little small.  Generally though I look for two things focus acquisition and the subject becoming more defined or snapping to focus.  The minimum focus distance is measured from the sensor plane and as stated above you are focusing on a virtual image, which is closer.  You can use this to Visualise  how far away you can focus:  https://oceanity.com.au/tools/virtual-image-calculator/ 

 

For a 6 inch dome (with a 3" radius of curvature ) at 20cm object distance from dome the virtual image is 8.1cm from the dome, which is as low as the calculator goes.  I would estimate the virtual image is 5cm from the dome with an object 10cm from the dome and it really should be able to focus on that.  If you were focusing on coral maybe the back of the coral head with coral branches against clear water had the better contrast and it focused there.  Just because it locked focus does not mean it focused on what you wanted to focus on.

 

Based on my Oly 12-40 which has the same more or less min focus distance you should be able to focus maybe 5cm from the port surface.  You could try assigning focus peaking to a function button and confirm it's peaking around the thing you want to focus upon?




#406773 ikelite 6" dome + old canon lens = no focus

Posted by ChrisRoss on 03 June 2019 - 08:32 PM

You could make it work with a diopter, the minimum focusing distance is 40cm so it can't focus on the dome virtual image, which will be about 20.8 cm from the dome surface for an object at infinity and probably around 14cm from the dome at 0.5m object distance.  The object distance is measured from the sensor when talking about minimum focus distance.  This assumes the dome is a 6" hemisphere.  If you don't understand dome port optics, the short explanation is that due to the being in water the lens does not focus on the object itself but on a virtual image of the object which is very close to the dome.  SO lenses have to focus down to around 30cm to be usable without a diopter with this dome.  Larger domes have the virtual image further away so more lenses are compatible

 

Looking at the ikelite port chart, the 35-80 lens is listed as requiring a +4 diopter with an 8" dome, so that might be a good starting point.  You can test the diopter by checking that it focuses on objects between 14 cm and 21 cm from the dome surface on land.  If you look at the ikelite website is says here: https://www.ikelite....-up-to-4-inches  that :"  Zoom lenses that do not focus to 12 inches (30 cm) require a +4 diopter close-up lens."

 

A flat port doesn't allow you to go very wide and will degrade images a little at the edges more so as you go wider.   The 35-70 would be equivalent to about a 45-90mm lens through a flat port due to the magnifying effect that a flat port has. 

 

There's nothing magic about lenses listed, they are just the ones that ikelite has tested.  if they only focus down to 40cm, just add a diopter.  The other requirement is not to be more than 100mm long according to Ikelite website. If they meet those criteria, you could try them.    The other issue is whether you can find zoom gears for the lenses.

 

I don't know what you are planning on shooting with the 35-70, it's not very wide and doesn't focus very close so even with the diopter macro is difficult, and a bit narrow for scenic.   I would suggest a 24-85 might be more generally useful and would do all the 35-70 does plus being able to shoot wider for scenic, fish schools etc.  It would probably be available quite cheaply second hand.    I would guess the 35-70 may work well for fish portraits.  It all depends on what you planning on shooting with it.




#406517 Olympus 8mm Fisheye with larger dome via N85 - N120 converter

Posted by ChrisRoss on 23 May 2019 - 08:54 PM

ChrisRoss, extremely clear explanation. Actually I got a used PTEP14 so Im planning to get my EM1 Mark II underwater and expand a little bit my options. I have been shooting mostly Fisheye and Macro for the last 3 years and start feeling a bit limited with the Fish Eye.

I am thinking that with a 170mm+ dome in the PTEP14, I can fit both the Olympus 7-14 as well as the 12-40 (I would love to have the versatility of the 12-40 with zoom gear...).

There are still a couple of the aspects where Ive found little info. One is regarding performance of 12-40 in higher focal lengths behind a dome. The other one is regarding semi-domes performance, as AoI officially recommends a semi-dome for the 12-40.

Thanks again for the very relevant input.

Sent from my SM-N960F using Tapatalk
ChrisRoss, extremely clear explanation. Actually I got a used PTEP14 so Im planning to get my EM1 Mark II underwater and expand a little bit my options. I have been shooting mostly Fisheye and Macro for the last 3 years and start feeling a bit limited with the Fish Eye.

I am thinking that with a 170mm+ dome in the PTEP14, I can fit both the Olympus 7-14 as well as the 12-40 (I would love to have the versatility of the 12-40 with zoom gear...).

There are still a couple of the aspects where Ive found little info. One is regarding performance of 12-40 in higher focal lengths behind a dome. The other one is regarding semi-domes performance, as AoI officially recommends a semi-dome for the 12-40.

Thanks again for the very relevant input.

Sent from my SM-N960F using Tapatalk

The EM-1 II is great UW, AF is a big improvement over the EM-5 II, C-AF plus tracking works very well.  The 12-40 is very good at all focal lengths some examples:

 

http://homepages.ihug.com.au/~chrisx2/images/GiantCuttlefish20.jpg taken at 12mm

 

http://homepages.ihug.com.au/~chrisx2/images/Wobbegong4.jpg taken at 40mm both near full frame just a slight crop for composition.  I use it behind the Zen 170mm dome

 

http://homepages.ihu...lackEyeGoby.jpg  this is very close at 40mm

 

There are a number of dome options for the PT-EP14 including Olympus's own dome, this is the system chart:  https://asia.olympus...t/000085635.pdf




#406413 Online critter ID

Posted by ChrisRoss on 20 May 2019 - 03:32 PM

I use this a bit:

 

http://skaphandrus.c...-identification

 

if you contribute photos you get points to unlock some of the groups, others like nudis are free.  The nudi key is successful maybe 50% of the time.




#406295 Diopter for WA?

Posted by ChrisRoss on 15 May 2019 - 01:27 AM

You don't need a diopter for this lens,  as it focuses close enough by itself.  A diopter is used for WA if the lens can't focus close enough to focus on the virtual image formed by the dome which is about 3 dome radii away from the dome surface.  If the lens can already focus on this a diopter does not help.

 

The S&S lens helps by bringing the corners into focus, the virtual image is curved and the corners are closer and you need to stop down to bring them into focus.  The S&S lens helps by partly correcting this curved image so you dont need to stop down as much to bring the corners into focus.




#406134 Strobe Failure A note of caution

Posted by ChrisRoss on 08 May 2019 - 10:46 PM

Still air is actually quite a good insulator, and most insulating materials work by trapping small pockets of still air- just look at double glazing - the insulation comes from trapping air between the panes.  Plastic has significantly lower conductivity than metal which is why pots and pans often have plastic handles, you can pick them up without protection on the stove.  INON now has a heat sink onto which all of the heat producing components are attached and that extends to the outside to conduct heat to the water.  Retra makes their housing from aluminium to assist with shedding heat, so these manufacturers are attempting do something about the heat problem.  INON Z-330 heat sink is described here:  https://www.backscat...derwater-Strobe

 

I suspect that the ring shaped tubes are significantly more expensive so they use off the shelf straight tubes to build to a price.  The ring flash also has more surface area so probably runs cooler than the straight tubes.




#405617 Durability of Nauticam handles

Posted by ChrisRoss on 21 April 2019 - 03:02 PM

I've found my Nauticam flextray quite solid.  You do need to pay attention to periodically tighten the screws and use the stainless brackets between the top of the housing and top of the tray handle, which significantly strengthens the whole setup.   I also grease all of my screws to help guard against corrosion. 




#405146 Importance of auto-off on focus light?

Posted by ChrisRoss on 10 April 2019 - 09:48 AM

If you have the capability use back button focus, you can normally assign that to one of the function buttons, then you have the best of both worlds.  Use the function button to focus then don't touch it again till you need to.  That way if you find a subject that's really close you can focus on it if need be.




#405069 Importance of auto-off on focus light?

Posted by ChrisRoss on 08 April 2019 - 07:57 AM

certainly there are situations where you could make use of the focus light when shooting macro, however the OP specifically mentions CFWA where it may present some issues .

 

I'm also sure you could get the focus light to show if for some reason you shot high ISO and/or wide aperture, but that's not a normal situation in UW photography where the strobes are set to overpower ambient light.  It could be an issue  for example shooting a small sensor compact at f2 (quite common in such cameras like theTG5), but on a m43 I would think you'd mostly shoot around f8 at least if behind a dome port.

 

The explanation as to how the light is able to switch off is that the duration of the strobe exposure is much shorter than the shutter speed which sets the ambient light exposure.  So if the light turns off for say1/8 of a second after receiving the signal to shut down, likely the light is only present for something around the duration of the strobe exposure, so a very short time compared to the total time the shutter is open.




#405052 Importance of auto-off on focus light?

Posted by ChrisRoss on 07 April 2019 - 06:05 PM

The "focus" light on your strobe is of little use as it has a narrow beam and one of the first rules of UW photography is don't point your strobe at your subject.    Your focus light does not need to be very bright at all, I find a 350 lumen INON UW torch does a good job and with that low power level it's quite a few stops under you main exposure s just does not show up in the image.  I have used such a ight mounted to the cold shoe with both the EM-5 Mkii and EM-1 MkII and it just works,




#404792 Sony RX100 VA - Nauticam package

Posted by ChrisRoss on 29 March 2019 - 11:11 PM

The shutter release does make things easier.  Definitely get the the vacuum valve/pump, gives great peace of mind!  It should be a good little package.

 

Did you see this article:  https://www.backscatter.com/reviews/post/Backscatter-Best-Underwater-Compact-Cameras 

 

The Nauticam housing with tray is the same price for both the LX10 and RX100VA so they might allow the same package for the LX10 as the RX100VA - wouldn't hurt to ask if it was of interest.  Note the link you provided states ships to the Americas and the Caribbean, and you don't appear to be located there.




#404743 Strobe Advice

Posted by ChrisRoss on 27 March 2019 - 09:48 PM

The figures are fairly straight forward for strobe power, the Z-330 is GN 33 and the D200 GN 20.  This is about 1 1/3 stop difference in output at full power  They both have a 110° field without diffusers. 

 

The YS-D2 is GN 32 - very close to the Z-330 you might think, but it has an 80° beam so its not apples to apples.  With the 100° diffuser it reduces to GN 24 and the 120° difffuser is GN 20. 

 

If you add the bundled diffuser to the Z330 you lose 1/3 stop so it's about GN 26.  So more power and a wider beam than the YS-D2 with 100° diffuser.

 

The INONs seem to have a very good reputation for reliability, I have been using my Z-240s for about 3 years now with no problems.  The manual is totally confusing, but a plain english guide is here:  https://reefphoto.co...-inon-strobes-1

 

The D200 is very new so probably not much data available, I would suggest putting your name down for a Z-330




#404654 Shiprock, Sydney Australia

Posted by ChrisRoss on 24 March 2019 - 07:49 PM

One of the best regarded divesites in Sydney is Shiprock.  The site is on Port Hacking to the south of Sydney and the entrance is in suburbia, surrounded by expensive waterfront homes, it has an amazing array of life and being an aquatic reserve  fish are plentiful.  This is a shore dive and there are steep steps down a cliff face to reach the entry point and the site features a wall running from about 7 to 15m deep.  It is subject to strong tidal currents and needs to be dived on a slack preferably high tide.  Here is a google maps link:  https://goo.gl/maps/Nq2mRe95rYu

 

Had a really nice dive there last Friday and here's some pics, descriptions below the pic  All taken with OM-D EM-1 MkII and Panasonic 30mm macro - Nauticam housing, INON Z-240 strobes:

 

PineappleFish3.jpg

Pineapple fish are nocturnal and have a light producing organ that assists with their hunting.  Shiprock is one of the few spots they are regularly found around Sydney dive sites.

 

SeivePatternedMoray2.jpg

Sieve Patterned Moray, less common than the regularly seen Green Moray

 

RingscaleTripleFin2.jpg

Ringscale Triple Fin, a small fish that claims sections of rock as territory, common at Shiprock but not so common elsewhere,

 

SixSpineLeatherjacket4.jpg

Six Spine Leatherjacket, quite common of many dive sites, but tend to be skittish, this one is about 300mm long so a bit of a challenge for a macro lens

 

PygmyLeatherjacket5.jpg

A Pygmy Leatherjacket another common fish around Sydney they seem to have their tail curled around semi permanently

 

EasternFrogfish.jpg

Eastern Frogfish, an ambush predator hiding under one of the many ledges at Shiprock

 

Doriprismatica_atromarginata6.jpg

Doroprismatica atromarginata, quite common around Sydney and the only Nudi I found this dive,  At other times the variety of nudis is much greater.

 

BlotchedHawkfish2.jpg

Blotched Hawkfish, Shiprock is the only Sydney dive site I see these regularly




#404624 Smaller alternative to Nikon FX (m4/3)

Posted by ChrisRoss on 23 March 2019 - 06:22 PM


 

There is a misconception about how WWL and WACP work:

 

 

Conversion lenses offer a virtual image that is parallel to the sensor, so remove the DOF issue that is a problem with dome/lens combinations. The WACP can be used with high-resolution cameras at very open apertures (f/4) and still give excellent corner results. 

 

There's not really any misconception, I'm fully aware of how the WACP functions - it's basically a field flattener, bringing the corners of the curved virtual image into focus at the same time expanding the field of view, probably not so good with choice of words.  I recalled reading the reviews of the WACP and WWL  and was not sure exactly how low you could go with aperture and seemed to recall f8 being touted as a limit.   Since posting that I went and reviewed the article in UWP 99 to confirm my recollections.    The UWP 99 can be found here:  http://www.uwpmag.com/?download=99  

 

On p42 you can see peak image quality in the corners occurs at f16 for the chosen rectilinear (nikon 14-28) as does the WACP albeit at higher resolution and the WACP resolution drops with aperture and is equal to the 14-28 at f16 when the WACP is at f8, basically a 2 stop advantage. f 5.6 is certainly usable.  So aperture does impact corner quality still, whether this is a limitation of the WACP/WWL or the kit lens being used is less certain.

 

The main purpose of the post was to explore any aperture advantage that might be obtained in m43 over full frame.  On p42 you'll also see data for the WWL vs the Oly 7-14mm,  The 7-14 peaks at f11 and the WWL is equal or better than the 7-14 down to f5.6 and again there's a 2-stop advantage.  

 

The whole idea behind the sort of comparison is that when people see the dynamic range, noise and other  numbers in isolation the numbers quoted are the numbers for base ISO, but the Noise, DR and colour depth all reduce as ISO goes up.  If you can operate 2 stops wider open you can use two stops better ISO on m43  and claw back part of the full frame advantage.  However is you can get to f5.6 to f4 of full frame that advantage is very much reduced to non-existent as the lenses being used will be wide open.   It's still not as good as full frame but if you are aware and adjust your aperture and ISO appropriately it closes the gap.  Of course is you shoot your full frame at base ISO it leaps ahead. 

 

It will be interesting to follow developments in water contact optics, the WACP certainly provides excellent performance at a price in both purchase $$ and weight.   Maybe a hybrid between the Sea and Sea internal corrector and a water contact optic? 




#404599 Nauticam GH5 your port and lens. Why?

Posted by ChrisRoss on 22 March 2019 - 06:05 PM

This post may be relevant:  http://wetpixel.com/forums/index.php?showtopic=63783 in here Phil Rudin states that the corners are much better using the Zen 200mm dome compared to the 170/180mm domes, though unfortunately that dome appears to be discontinued.  This seems plausible to me as one day i trilalled my Panasonic 7-14 to find the entrance pupil location and as far as I can figure it appears to be 20-25mm forward of the optimal position when using the Zen DP-170 typeII.  A further check with a little trigonometry revealed it was positioned forward to prevent vignetting in the 170mm dome.  This is relatively easy to check.... the radius of curvature of the Zen DP-170 is 110mm , 110mm measured from the dome is 15mm from the port bayonet end and there is no way the entrance pupil is that far back.

 

If you do more trig , you can calculate the height of the sphere segment for the 170mm dome and the 200mm dome, which both have a 110mm radius of curvature and you will calculate h=40mm for the 170mm dome and h=64mm for the 200mm dome, so with the same extension the 200mm dome is 24mm further forward from the lens which should place the entrance pupil just about right on the radius of curvature of the dome, which would  explain better corners with the 200mm dome.  Both domes are the same radius, however so the virtual image is the same radius, but it is further away by the difference in dome segment height making it easier to focus upon.  This is for the ZEN 170 vs the 200mm dome, seems you have the Nauticam 180mm dome which may be slightly different and the location of the entrance pupil for the Oly 7-14 will be different and you would have to calculate that for your self, but I doubt the entrance pupil is way at the back of the lens. 

 

It seems manufacturers pick a compromise between vignetting and positioning of the entrance pupil, probably on the basis corners are good enough and the situation rapidly improves once you zoom a little as you are no longer trying to get the very far edges of the virtual image in focus.  This seems essential on the partial hemisphere domes in the 170-180mm size range as you need to push the lens far enough forward to see over the edge of the dome.  As to the original problem you may find the corners improve by zooming in to 8-9mm or so and reserving 7-8mm for blue water subjects where the corners are water?

 

On the 60mm macro lens, the dial is there to help with AF keeping it within a certain range.  The 1:1 setting is spring loaded and you use it to send the lens to 1:1 focus and have AF take over from there.  MF is really not practical due to the gearing on the focus dial being so high, you really need multiple spins on the housing focus knob to see any change at all in focus.  The only approach is AF on back button focus then use a Fn button to activate zebras and rock back and forth to get/hold focus, DOF is very shallow at 1:1 so absolute steadiness in needed to keep focus where you want it and any sort of surge complicates matters more as there's no way to keep up with it.  This tends to mean you need to back off for a wider view and greater DOF.  I ended up buying the 30mm macro as most subjects I shoot require 1:2 or less magnification - nothing magical about 1:1 just use the magnification needed to frame your critter.  To explain the 30mm macro will do 1:1 but the subject is too close to the port, maybe 10-20mm from the glass.  I'll swap back and forth depending on the dive site and what I expect to find.   Keep in mind I shoot stills so just need to squeeze the shutter at the right moment, video needs to keep the subject framed for many seconds without losing focus making it even more challenging. 

 

I'm not sure what you are shooting in the way of macro, if it's not super small the 30mm may be easier to handle and certainly snaps to focus better on my EM-1 MkII.  I have the Panasonic 30mm macro.