8-15 on a crop, but not the recommended ext. rings?

As I'm slowly making the move to FF, I've yet to upgrade my housing.

I did manage to pick up the Nikon 8-15 fisheye, but I also have my Tokina left over until I make the final jump. It hasn't arrived yet.

Nauticam recommends the following:

I have the following ext. rings and domes:

* 20mm

* 40mm

* 8.5" dome

* 4.33" dome

I did contact Nauticam and they said they have recommended options as above, but says slight deviation may be possible. Would the following work, would it vignette depending on the zoom, or would it optically be quite bad?

* D500 + 8-15 + 40mm ext ring + 4.33" dome? (Nauticam suggests 30mm here, and not 40) 

* D500 + 1.4x TC + 8-15 +  20mm ext ring + 40mm ext ring + 4.33" dome? (Nauticam suggests 50mm here, and not 60)

I presume with the above it will either affect the useable zoom range or IQ? The other option is that I use my Tokina exclusively for the 4.33" dome work, and use the 8-15 for the 8.5" dome.

@TimG I know you've got this one so I'm shamelessly tagging you here  

Cheers!

Generally less extension is more likely to work than more.  The concern is vignetting, which you can check for on land.  First zoom the lens to the point where it fills out the frame which should be 10-11mm focal length then try it in the 4.33" with 40mm and see if it vignettes.  If it does vignette try it with the 20mm extension to see that it has enough clearance to the dome.  I suspect it would work reasonably well.  In fact the ikelite port charts list the compact 8"dome with these fisheye lens which is a really flat dome section and the only way they avoid vignetting is placing the entrance pupil well forward of the the centre of curvature of the dome.  The results won't be absolutely perfect but should be adequate until you switch over to FF. 

If it works with the 20mm extension and bare lens then using the 40mm alone (20mm more extension which is 1.4x thickness) places the lens in the same relative position and should also be fine.

Thanks @ChrisRoss that's useful.

I was thinking of doing the full gamut of testing in the bathtub but I suspect this will do, and only test a few combos in the tub.

I did have a look at the wetpixel live chat about the 10-17 vs 8-15, and I'm hoping at least for the big dome shots, the 8-15 will provide some good results, even if it's on a crop sensor.

1 hour ago, sinetwo said:

@TimG I know you've got this one so I'm shamelessly tagging you here  

 

No worries! Always happy to try and help.

I must admit I find it hard to spot a significant difference between the Tokina 10-17 and the Nikkor 8-15 on the D500. With or without the TC1.4.

Alex M and Adam discussed the differences on one of their videos a while back. If I remember correctly, they came to the conclusion that the difference in quality on DX did not merit the difference in price. I suspect I tend to use the 8-15 when I have one of those "it must be better cos it costs more" moments.

I do like the 8-15 on the D500. As you probably know already, on an FX sensor the 8-15 is effectively two lens (8mm circular FE or a 15mm FE) and not really a zoom. But with the DX-sensored D500 it really is a useful zoom. But a real difference from the 10-17? Hard to spot.

I tend to use the Tokina with a 100mm domeport and the Nikkor with an 8" domeport (Subal ports) - but there is no technical reason for this. 

On EXRs I set up as follows:

Tokina 10-17mm

DP100 + EXR13

DP100 + EXR33 with TC1.4 DX

8" DP + EXR18

8" DP + EXR20 + EXR18 with TC1.4 DX

Nikkor 8-15mm

8" DP + EXR20 

8" DP + EXR20 + EXR 18 with TC1.4 DGX

Thanks Tim, I think i'll do the next trip with the Tokina 10-17, then look at the 8-15 when I upgrade my camera housing

1 hour ago, sinetwo said:

Thanks Tim, I think i'll do the next trip with the Tokina 10-17, then look at the 8-15 when I upgrade my camera housing

Whatever the Tokina might produce topside, (horrible!) it is wicked underwater..... I'd say your plan is a good one.

On 6/23/2023 at 10:12 PM, sinetwo said:

Thanks @ChrisRoss that's useful.

I was thinking of doing the full gamut of testing in the bathtub but I suspect this will do, and only test a few combos in the tub.

I did have a look at the wetpixel live chat about the 10-17 vs 8-15, and I'm hoping at least for the big dome shots, the 8-15 will provide some good results, even if it's on a crop sensor.

I really don't think you need to test UW, it will work fine maybe not quite the same corner performance, if it doesn't vignette that's the main concern.

5 hours ago, ChrisRoss said:

I really don't think you need to test UW, it will work fine maybe not quite the same corner performance, if it doesn't vignette that's the main concern.

Agreed, I do however have the optimal set up for the D500 + Tokina, so I think i'll stick to that for this trip, then experiment. If the corners are worse on the 8-15 with Crop, then I think I'd definitely want to stick with Tokina + 8.5" dome for splits. I'm less concerned about corners with the CWFA macro 4.33" approach.

Thanks for all your input.