Tips to avoid blurry edges ?

Hi

I am using Nikon Z62, Nikon 8-15, Isotta housing and 4.5 inch dome port. 

I have noticed that I can't avoid blurry edges in the frame. Is it because I am using a small dome ? 

A smaller aperture can reduce it ?

what can I do to minimize this effect ?

Thanks

Ido

Hi Ido

If you search around Wetpixel you'll find lots has been written on the topic of soft edges when shooting wide-angle..

Generally for wide-angle imagery with a full frame sensor you need a big dome: 180 at least but preferably 230mm. This is certainly the case for rectilinear lenses. And, yes, you have to stop down - and even then, sharp corners are not a given.

For fisheyes - and the Nikkor 8-15 certainly fits in this category - a smaller dome can work fine. What aperture were you using? Stopping down to something smaller would certainly be the first thing to try. F11, f16? 

If you are still getting soft corners then the only option might be a larger dome.  Subal, for example, does recommend using either their 180mm dome or the 230mm with the Nikkor 8-15mm. 

I've found that lens has good corners on a D500 (APS-C sensor of course) with a 4" dome. But maybe that isn't the case with FF.

Thanks. I will make more tests with smaller apertures.   

Yep, worth trying for sure. 

After that..... could well be a bigger dome.

Well done on your first pics, by the way. A good start! Hope you enjoyed the trip.

Your dome would be OK for FF at 15mm but for MACRO shots. Maybe OK at 8mm but you need to be able to remove the dome shade if it has one.

A great many people use small domes with fisheye lenses even on full frame and typically they talk about using f11-16.

What aperture is the image you attached?

One thing to be aware of that while you have very good depth of field from a fisheye it's not infinite. You have to think about what you are focusing on, I had that problem on wall dives, there was wall in very close to the camera but the subject was maybe 1m away.    The subject was sharp and things in the right hand corner were sharp, but the left corner where the wall was very close had more extensive blurring.  If the lens focuses on distant elements the closer elements can fall outside the depth of field available.  So you need to focus on something a little closer to the lens.

This may or may not be your problem, but if you are going to test, take shots square on to the reef or point straight down onto the sandy bottom.  It will give you a better idea of how the lens is performing.

Thank you. All the picture that I took was around f8 (7,8,9) - So there is place to stop down. I will test this again next time. 

The corners look quite bad for f/8. I would check your extension rings too. It may be that the lens is not correctly placed (too far forward) in the dome. Bear in mind that the length of the FTZ adaptor need to be taken into account when selecting extensions. 

Adam

I do have an extension for this setup as recommended from Isotta. 

1 hour ago, ido said:

I do have an extension for this setup as recommended from Isotta. 

Hard to tell what ring that is, the port charts state that the ring to use with 8-15/FTZ adapter and 4.5"dome  is the 26mm with gear, item number 2343, which is this item:

https://www.isotecnic.it/en/extension-ring-with-zoom-for-nikon-z7-6

This is exactly what I am using here. I will contact Isotta and ask for advise. 

I had missed that you are using a 4.5" dome. Sadly this won't really work on full frame. It can be used for extreme CFWA, when the subject is almost on the port, but otherwise, it is difficult to get decent corners. For most images, like the one above, you really need a 7" or so dome to get good corners.

I would be interested to see how the lens looks without an extension with the dome. Isotta recommends the 26mm extension as this allows sufficient room for the FTZ adaptor, but the adds a 20mm extension with their other domes. My guess is that adding the same extension would improve the corners with the small dome, but it may still prove hard to shoot given the actual dome size.

Thanks. If I want to have a good balance compact setup/quality - Is this: https://www.isotecnic.it/en/wide-angle-dome-port-b120/ports-for-b120/dome-port-6,5-crystal-b120-detail  can work for wide angle ?  (6.5 inch with extra extension )  

Or I should go bigger and heavier ...?

For wide angle or fisheye?

Nikon 8-15 fisheye. I am only on the 15 mm 

5 hours ago, adamhanlon said:

I had missed that you are using a 4.5" dome. Sadly this won't really work on full frame. It can be used for extreme CFWA, when the subject is almost on the port, but otherwise, it is difficult to get decent corners. For most images, like the one above, you really need a 7" or so dome to get good corners.

I would be interested to see how the lens looks without an extension with the dome. Isotta recommends the 26mm extension as this allows sufficient room for the FTZ adaptor, but the adds a 20mm extension with their other domes. My guess is that adding the same extension would improve the corners with the small dome, but it may still prove hard to shoot given the actual dome size.

I am guessing using a different extension is not an option for Isotta as it notes the 26mm is specifically for using F lenses, I believe the zoom knob is used with F mount lenses standard zoom gear.  The FTZ adapter adds 46.5 - 16mm = 30.5 mm of extension, so if the camera flange is in the same position relative to the port the lens would be 4mm further forward - but it's quite possible Isotta moved the flange back 4mm relative to the port mounting surface.   The extra 20mm extension is consistent  for the 6.5"and larger domes between the port charts.

On 12/8/2021 at 2:48 AM, ido said:

Thanks. If I want to have a good balance compact setup/quality - Is this: https://www.isotecnic.it/en/wide-angle-dome-port-b120/ports-for-b120/dome-port-6,5-crystal-b120-detail  can work for wide angle ?  (6.5 inch with extra extension )  

Or I should go bigger and heavier ...?

 

I would first try stopping down some more.  I know Adam likes a larger dome for his fisheye lenses, however you might be happy with the results at f11-13?  Test it at those f-stops and see what it looks like - be sure the test shots are square on to the surface- shooting a sandy bottom might be a good option to test.

Thanks. I will probably test it next month and I will report the results here as usual..  

The 8-15mm is a fisheye lens, not a wide angle. It may sound pedantic, but it makes a big difference for port size.

For fisheye, a 6.5" dome should be OK. You can use the 4.5" of course, and it is great for shooting when you are very close to a subject, but I don't think that you will get good corner performance for reef scenics etc with it. While stopping down will help, this will compromise in lots of other ways, and limit your options. 

My guess is that Isotta's port chart reflects this. For very close focus, the goal is to get the lens as far forward in the dome as possible, in order to minimise lens to subject distance at the compromise of corner performance. It would be interesting to try a 20mm extension. 
 

1 hour ago, adamhanlon said:

 

Thanks. This is probably what I will buy: A 6.5 dome port with 20 mm extension that will be assembled on the 26 extension that I already have. I don't like so many extensions in one setup - But probably I don't have a choice. In this case my 4.5 dome will be used only as a backup dome..