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EvilOtter

Diopter Inside a Dome Port

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Posted (edited)

Hi all,

I am currently on my way to upgrading to a mirrorless system based on the Panasonic G85 in an Ikelite DLM/B housing (6961.08). I am already equipped for wide angle using the Olympus 8mm fisheye in an 8” dome port (5516.81) and for macro using the Olympus 60mm macro in an extended flat port (5516.50). My mid-range, run-and-gun option is the Panasonic Leica 12-60mm in a 6” dome with zoom (5515.15) and a 1.2” extension (5516.65).

Unfortunately, according to Ikelite’s DLM/B port chart, the 12-60 will slightly vignette at 12mm. I spoke with John at Ikelite and, although he was extremely helpful, he was not immediately aware of a port/extension combination for the 12-60 that would not vignette. That said, Backscatter recommends the use of a +2 close up lens with this configuration.

I understand that the principle of a low-strength diopter behind a dome port is usually to improve corner sharpness by moving the virtual image closer to the lens. However, my questions are as follows:

1. Is the addition of a diopter likely to remove the vignetting?
2. What will be the impact on field of view? Will I still get 12mm?
3. Will I still be able to focus to infinity?
4. Can I use step a down ring with a diopter, without impacting image quality, if I want to fit it to a smaller lens?
5. Are there other options to address vignetting or do I just live with a slightly crippled lens at wide?

Thanks in advance for your kind assistance and advice!

Doug

Edited by EvilOtter

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5 hours ago, EvilOtter said:

Hi all,

I am currently on my way to upgrading to a mirrorless system based on the Panasonic G85 in an Ikelite DLM/B housing (6961.08). I am already equipped for wide angle using the Olympus 8mm fisheye in an 8” dome port (5516.81) and for macro using the Olympus 60mm macro in an extended flat port (5516.50). My mid-range, run-and-gun option is the Panasonic Leica 12-60mm in a 6” dome with zoom (5515.15) and a 1.2” extension (5516.65).

Unfortunately, according to Ikelite’s DLM/B port chart, the 12-60 will slightly vignette at 12mm. I spoke with John at Ikelite and, although he was extremely helpful, he was not immediately aware of a port/extension combination for the 12-60 that would not vignette. That said, Backscatter recommends the use of a +2 close up lens with this configuration.

I understand that the principle of a low-strength diopter behind a dome port is usually to improve corner sharpness by moving the virtual image closer to the lens. However, my questions are as follows:

1. Is the addition of a diopter likely to remove the vignetting?
2. What will be the impact on field of view? Will I still get 12mm?
3. Will I still be able to focus to infinity?
4. Can I use step a down ring with a diopter, without impacting image quality, if I want to fit it to a smaller lens?
5. Are there other options to address vignetting or do I just live with a slightly crippled lens at wide?

Thanks in advance for your kind assistance and advice!

Doug

It seems strange that a 12mm lens would vignette in an 6" dome, the cause would be that the extension is too long placing it too far back inside the dome.  The solution would be the next smallest size extension, though unfortunately does not look like Ikelite makes one. 

Regarding the diopter, this seems like a relic from yesteryear, the only reason to use a diopter is so that the lens will focus a little closer and is used for an UW lens with a long minimum focus distance that can't reach focus on the virtual image.  The 12-60 has a min focus distance of 20cm - this is from the image sensor, so it will almost focus on the dome itself.  So in summary a diopter is not needed.

I don't see how a diopter could remove vignetting.  Do you have the equipment yet?  Looking through the port charts I see the GX85 DLM-A housing for the GX85 does not report vignetting but the DLM-B does - seems quite strange, but if I've read their website correctly this seems like the only solution.  The issue is that to zoom you need a port with a zoom gear - the housing does not have zoom control and the only port with a zoom knob they offer is the dinky little 6" port.  I can see how that would vignette on you.

I see on Ikelite's website they offer a 5516 dome with zoom with 1" of extension built in- that is 0.2" less than using the 1.2" extension.  This would move the lens forward in the dome and might work to reduce the vignetting it's the 5516.17 - you could aks if that is compatible with your 12-60???

It also looks like the olympus 12-40 is similar but maybe less severe - it mentions vignetting due to image stabilization - the lens sensor moves in Oly bodies which would not happen with a Panasonic body without in-body IS.  It is a great lens also just a touch less reach.

Maybe you could discuss these options with Ikelite or one of the retailers?

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Hi Chris,

Thanks very much for your thoughtful response. I was also of the understanding that the vignetting was caused by the port being too long. I still don’t understand why Backscatter recommends the use of a diopter with many of lenses in DLM/B ports.

In my discussions with Ikelite, John mentioned that they tested the Leica 12-60 before the company developed the shorter 5516.16 and 5516.17 ports. However, since they no longer had the lens, he was not able to test it. He offered to do the testing if I sent him my own lens, but I have not yet purchased it. He also did some testing with the Lumix 12-60 and found that it does not vignette in the 5516.16 port.

I have considered the Oly 12-40 Pro and the Oly 12-45 Pro but I would lose the advantage of dual IS, which is important to me for run-and-gun shooting. Also, the Leica 12-60 has greater reach and a higher magnification ratio, which are also important to me for semi-macro.

Note that I have purchased all of the gear for the wide and macro configurations but I have not yet purchased anything required form the standard zoom. I do own a copy of the Lumix 12-60 kit lens so I could always use that in the 5516.16 port. That said, my preference is to use the Leica 12-60, which is faster, sharper and has a slightly higher magnification factor.

To this end, maybe I should reframe my question as follows:

Is anyone aware of a port/extension combination that will allow the use of the Leica 12-60 in an Ikelite DLM/B housing?

Thanks,

Doug

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It's actually the extension that is too long.  If you look at Ikelite's webpage you'll see the 5516.17 is a longer port as it includes built in extension.   https://www.ikelite.com/collections/dlm-lens-ports?sort_by=price-descending

I would think that the chances of the 12-60 not vignetting in a 5516.17 used with no extension tube are very good as the total extension is 0.2" shorter and the report is only slight vignetting .   The Oly 12-40 lens is about 87mm long at 12mm compared to the Leica 12-60 being a reported 86mm.  The Oly is reported to only vignette due to IS sensor movement and the 12-60 says slight vignetting, which means that you only need to move the port back towards the lens a small amount to remove vignetting. 

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Hi Chris,

This makes sense to me. John at Ikelite suggested that the Leica 12-60 would probably fit in the 5516.17 port with no extension but he could not assure me that it would not vignette. I would need to send him a copy, which I don’t yet own, for testing.

I am also confused at his statement that the smaller Lumix 12-60, which I do own, did not vignette in the 5516.16 port, which is 0.375” longer than the standard 5516.15 dome. According to the DLM/B port chart, the Lumix 12-60 vignettes tremendously in the 5516.15. How could a longer port address this? 

Ultimately, I would be happy using either one of these lenses but I am getting flummoxed by the lack of clear information.

Thanks,

Doug
 

 

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It does seem odd the Lumix lens is about 10mm shorter than the Leica, but in the 5516.15 port the front element will be 20mm further into the dome than the Leica lens is in the 5516.15 plus 1.2" extension,  so should not vignette at all.   Even in the 5516.16 it will be 10mm further into the dome. 

Seems like a typo or error in the port chart.

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Hi Chris,

That was my thinking as well.

Today, I was able to obtain a 5516.15 port and test it with my Lumix 12-60mm (the kit lens). It showed no vignetting at 12mm when I used it above water. I was not able to test it in water but I assume that the results would be the same.

I suspect that the Lumix 12-60mm may have been tested with the 1” extension, which is how the Leica 12-60mm is configured. I notified Ikelite and asked if they could validate this and, if correct, update the DLM/B chart.

In my view, the G85 housing would be more appealing to potential customers if they knew that they could use their kit lens in the cheapest dome with zoom while getting the benefit of dual IS.

Cheers,

Doug

 

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Just to close the loop on this thread, I would like to confirm that Ikelite has provided a new port recommendation for the Panasonic Lumix G Vario 12-60mm f/3.5-5.6 ASPH POWER O.I.S. lens for the DLM/B system. This involves the 5516.16 3.75” Extended Dome Port and the new 5515.28 Zoom Gear. This configuration provides zoom through the full range with no vignetting and improved corner sharpness as compared to the 5516.15 port. The zoom gear is currently available from Ikelite but is not yet listed on their website. I expect that it will be a few more weeks before it is listed by retailers but could probably be obtained by special order. 

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