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divegypsy

Member Since 07 Sep 2003
Offline Last Active Jul 27 2017 12:03 AM
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Posts I've Made

In Topic: DX to FX and back again

28 June 2017 - 06:13 AM

Hi all,

 

My two cents worth is that it isn't reasonable to compare the D500, which is a relatively new camera vs the D800, which is now 4?, 5? years old.  Why not wait for just a few months and compare the D500 vs the upcoming D820/D850 or whatever Nikon calls it.  It might be fairer to compare the D500 image quality vs the D810 in the DX crop mode. The D800/810 has slightly fewer Mpixels that the D500, but not so many fewer that its theoretical resolution would be much less than about 85% of the D500.  

 

As I see it the D500's primary advantages are the very enhanced auto-focus system and the newer image processor (X-peed 5), both of which are already in the F5 and will almost certainly be in the D8XX.  Thom Hogan and others are predicting that the D8XX will be released in only a few more months and will probably be about 46Mp, which means that in the DX crop mode you would get virtually the same Mp as the D500, and have the ability to switch up to the FX mode or the intermediate 1.2 crop mode at will.  Even during the dive. This would allow you to shoot the FX crop, the 1.2 crop, and the DX crop all on the same dive, with the same lens, while shooting the same subject.

 

I recently bought one of the new Nikon 8-15mm fisheye zoom lenses. In the past I have briefly shot a few topside shots with three different Tokina 10-17mm lenses.  Everything I shot with the Tokina zooms was so lacking in image quality that I felt shooting the Sigma 15mm f2.8 fisheye or the Nikon 16mm f2.8 fisheye and cropping the image to equal the coverage of any Tokina shot would result in better image quality.  Now that the Nikon 8-15mm lens has arrived and covers a very similar zoom range to the Tokina, but with much better image quality. By switching a Nikon FX camera from DX crop at 10mm, to the 1.2 crop and about 12mm, and then 15mm at the FX crop, you can get a stepped variation of the zoom range with progressively higher and higher image quality.  Or just shoot everything in the FX mode at 15mm and crop each image to suit.

 

I am looking forward to seeing and shooting with the D8?? when it arrives and will be perfectly satisfied with my D800's until it does.

 

Fred 


In Topic: Nikon 8-15mm in the house!

24 June 2017 - 07:36 PM

Hi Adam et al,      Some more comments on the fisheye lenses for Nikon and the camera you can use them on.

 

Adam, it seems you have misread my comment comparing the D500 to the D800/810.  I specifically wrote that I did not see a whole lot to be gained in image quality by using the D500 vs the D800/810 in the DX crop mode. I totally agree that the D800 in the FX mode will provide a significantly higher image quality than the current crop of Nikon DX cameras including the D500. And that is one of the reason's I shoot an FX camera. 

 

However, you have made the comment, "Strictly technically, the Sigma does actually focus closer than this lens (by 1cm). I note that Nikon list the FOV of the lens at 175° at 15mm on FX."  If you look at the lens specifications, as provided by the lens manufacturers, the Sigma lens may focus that 1 cm closer. However this lens specification distance is usually measured from the subject to the film plane or sensor plane in the camera body.  But underwater, and behind a dome port, how close to the front of the lens you can focus (which might be called the working distance) is more important due to the fact that with the dome port you are focusing on virtual images that are much closer than the actual subject. And with a small diameter dome port, those virtual images are quite close to the dome itself. The fact that the Nikon fisheye zoom is physically quite a bit longer than the Sigma fisheye means that at minimum focus, the Nikon lens focuses closer and provides a larger image (more magnification) than does the Sigma.  

 

I shot a couple quick comparison shots with the two lenses at the minimum distance at which each lens could focus and the camera still fire when shooting with my D800 set to single focus auto-focus with being in focus the priority. To do this, I started with the lens almost touching the little spice bottle and then backed it away in tiny increments until the camera was able to shoot the picture.  Here are the two shots.

 

Attached File  Nikon Fisheye zoom @ 15mm .jpg   127.31KB   15 downloads

This is the image shot with the Nikon fisheye zoom at minimum focus and at 15mm

 

Attached File  Sigma 15mm f2.8.jpg   126.92KB   15 downloads

This is the image shot with the Sigma 15mm fisheye at minimum focus

 

As you can see, the vertical height of the little bottle is not completely shown in the image taken with the Nikon fisheye zoom.  But there is space above the top and bottom of the bottle in the Sigma lens image.  I made paper "feeler gauges" to measure the actual space between the front element of each lens and the bottle.  The distance between the Nikon zoom's front element and the bottle was 24mm.  The distance between the Sigma's front element and the bottle was 51mm. I have not had the opportunity to shoot this comparison underwater, but will when I get home and can try both lenses behind both the Seacam wideport and the Seacam fisheye macro port.

 

Something that also shows in these two shots that I was not expecting is that if I look at the background of the Nikon lens vs the Sigma, the overall coverage with the Nikon lens is a bit wider than that of the Sigma lens. I would have expected there to be less difference as the glass bottle position remained constant and thus the Nikon lens was a tiny bit closer to the background as well as being 27mm closer to the bottle. 

 

So I would conclude from these images that the Nikon zoom is capable of providing a larger image (more magnification) of the subject at its closest focus than the Sigma fisheye can. And that at very close focusing distances, it includes a bit more of the background (is a little bit wider).

 

Fred


In Topic: Nikon 8-15mm in the house!

20 June 2017 - 10:31 PM

Hello Adam,  

 

Most of the thoughts I posted relative to the D800/810/820 and the D500 have relevance to this new fisheye lens as well as other lenses. And were made with the idea that if someone is thinking they might want to buy a D500 to get the "wider" zoom range of 180 degrees to 110 degrees that this lens provides on a DX camera, which is similar to the Tokina 10-17mm lens, that they could get the same zoom range by switching their FX camera to the DX crop mode and lose very little in comparison to a DX only camera. There have been many posts concerning the Tokina 10-17 which is a DX only lens unless you use it with a teleconverter which degrades its image quality. My feeling is that if you shoot a DX camera, and want a similar zoom range, the Nikon lens will provide this with considerably higher image quality. 

 

I did not shoot any pictures underwater at 8mm in the FX mode.  Everything I shot was at the 15mm (full frame fisheye) setting. As I wrote initially, I am not interested in circular fisheye images and I would have needed a zoom gear to make any changes while underwater, which I did not have at that time. My interest in this lens is because I can shoot it behind the wideport at 15mm with no vignetting whereas I cannot do this with the Sigma 15mm. And because it focuses so closely.

 

I had Nikon's own lens shade mounted on the lens when I took the picture of the octopuses that I posted. I shot similar images at f11, f16 and f22 and saw no vignetting in any frame. Since the lens is an internal focus design, that means the angle of coverage of the lens gets slightly wider as you focus closer and closer and the octopuses were only about six inches from the from of the wideport's glass surface.

 

The lens was behind the Seacam wideport with a 20mm extension ring between the wideport and the housing body.  If I get some free time I will take pictures of the housing with the port and extension ring in position as they were during the dive and post them.  I will also post a couple additional pictures that show that whereas the Sigma 15mm lens almost always exhibits some minor vignetting with the wideport, even without any extension ring, the Nikon lens does not.


In Topic: Nikon 8-15mm in the house!

20 June 2017 - 04:10 PM

I saw exactly the same vignetting, caused by the lens shade, when I shot topside pictures.  More extreme vignetting with the camera set to the full FX picture and less when I had my D800 set to the DX crop mode.  If you have an FX camera, like the D800 or D810, you can get the same picture area as Adam did by simply setting the camera to the DX mode.  

 

If you use the D800 or D810 in the DX mode you have a camera that shoots images very similar to the D500. I think it is about 16 Megapixels and has auto-focus spots covering nearly the whole image area. What the D500 offers is faster and possibly more accurate auto-focus, a faster frame rate which is of little use if you are shooting with strobes, and the larger image buffer which again is of little use if you need to wait for strobes to recycle. If Nikon's successor to the D810, D820?, appears with the rumored 46 Mp sensor (an upsized D500 sensor) the D500 will offer very little advantage, except size and weight and price, over the D820 when the D820 is used in the DX mode.  And it will offer more than double the Mp in the FX mode for higher image quality.


In Topic: Nikon 8-15mm in the house!

20 June 2017 - 04:17 AM

I received my Nikon 8-15mm lens about a week ago and have had it in the water once since then.  Because I shoot with a Nikon D800, my interest in this lens is as a close-focusing full frame fisheye lens.  I have very little interest in circular fisheye images.

 

I initially did a few topside shots comparing this lens to my Sigma 15mm f2.8.  My initial impression is that in dim light, the Sigma may pinpoint the focus in the center of the image a little better than does the Nikon lens. Probably due to the fact that the Sigma focuses at f2.8 vs f4.5 on the Nikon lens when set to the 15mm full frame.  But on those same test shots, the sharpness near the edges of the images were consistently better with the Nikon lens.

 

Underwater I have used both the Sigma 15mm and now the Nikon 8-15 behind the Seacam Wideport which has a radius of curvature of about 75mm, meaning that if you had that port as a full hemisphere, the diameter would be about 150mm or about 6 inches. I also own the Seacam 4" fisheye macro port, but pretty much stopped using it because you needed to cut off much of the lens shade on the Sigma 15mm when using this combination and therefore do not have it with me on my current trip.  I feel that cutting back on the Sigma lens shade resulted in too much image degrading flare.

 

With the wideport, I could use the Sigma 15mm with the manufacturer's full shade in place and although I did get slight vignetting at the corners of the image, I feel the image quality was better enough to use the lens this way.  With the Sigma 15mm, I use the wideport directly attached to my Subal housing body.

 

I switched to the Subal housing body for my D800's because I felt Subal gave me a much more complete set of controls to the D800 body functions than did the Seacam housing body and with the help of a good machine shop I was able to modify the port mount on my Subal housings to take my Seacam ports rather than buy a new set of ports.

 

Because the Nikon 8-15mm lens @ 15mm is physically longer than the Sigma 15mm, I am able to shoot the Nikon 8-15mm lens, with its Nikon lens shade mounted, without any vignetting when using the Seacam wideport in combination with a Seacam 20mm extension tube. With a 25mm extension tube, there may be a very slight amount at vignetting, but still far less than with the Sigma 15mm.

 

Below is one of the shots from my only dive so far with the Nikon 8-15mm lens. It shows a pair of small octopuses mating underneath the Edithburgh jetty in South Australia.  The image was shot late in the afternoon at 1/250th at f16 using ISO 3200 on my Nikon D800.

 

Attached File  _F8C8929.jpg   318.54KB   25 downloads

 

When anyone does tests to determine the nodal point of the 8-15mm lens, or any other lens, they should be aware that the nodal point of the lens lens can change with both the zoom setting and the focus point of the lens.  I found quite large differences when I did a series of tests on Nikon's 24-70mm f2.8 several years ago. Using the manufacturer's given nodal point is also likely to be at least slightly inaccurate for underwater use because the manufacturer's nodal points are given for lenses focused at infinity rather than at the close distances the lens is likely to focus at when used behind a dome port.