Dome test/corner shrpness -what am I looking for??

Hi follks,

I hope to try out my sigma 10-20mm wide angle lens and sea and sea nx compact dome with 40mm extension ring in open sea soon, but initially tried testing this combo in my bath tub last nite. The last two images were shot at f19 1/180sec with strobe at the 10mm end of the lens, the first image shot at the 20mm end of the lens at f16. Could anyone tell me what they think of these images as I havent a clue what I'm supposed to be looking for re: corner sharpness- or should I retest the lens conditions at different f stops.

What I just wish to ask is- what do you think of these images??? Any critique/advice much appreciated.

If you really want to see what's going on photograph a flat grid of some sort at different zoom settings and stepping through the f stops starting wide open.

and it really helps to have some text or detail in the corners so you can see the results at the different f/stops.

Check out this thread. Some charts on the 4th page.

Nice tub,

Steve

The flat white makes it very hard to tell what you have in the corners. You don't have to use a chart if you don't have one, but you need something with some detail at the edges.

Where can one find one of these test charts?

Also include diopters in your test series, such as +2, +3 (may be hard to find) & +4. My reference is Nexus 6.7"dome, Nikon 12-24mm lens, +4. Diopter really helps corner sharpness.

Where can one find one of these test charts?

The chart is here; http://www.graphics.cornell.edu/~westin/mi...33-reschart.pdf

If you want to go simple my buddy, the pro land photo guy, always uses a piece of newspaper taped to the wall. I printed up the chart as big and sharp as I could and then took it to an office place to get laminated. Seems to be holding up very well. Lots of ways to do it. Stephen Frink uses signs on a stand he can move around in the pool. Article linked here

Steve

Fantastic info. everyone-thank you so much- and thanks a million Steve for digging up the links!!

I will be learning the ropes of underwater dslr on vacation this year- hopefully- but I'd like to have as much 'bucket and spade work' done before I go on vacation first.

Just to confirm - I can perform tests on my dome port/wide angle lens combo set up on land as well as water- to give me an idea of corner sharpness??

If so- that would be even better/easier to do- and is a bit more eco-friendly than filling a bath tub with precious water.

One of the reasons I'm asking my original question is that I don't have a sea and sea zoom gear for my sigma 10-17mm wide angle lens as yet- but was intending to just simply do dives with the lens at various fixed focal lengths. I know this might sound like doing it the 'hard way'- but the way I see it is that although it would mean spending more cash to get a zoom gear- I'm inwardly wondering- do I really need to?

A second reason is I don't have easy access to a pool where I currently live-public swimming pools do not like lone camera divers period- and getting air for a tank is also a logistical pain in the butt for me too.

Any further thoughts much much appreciated

Damo

Just to confirm - I can perform tests on my dome port/wide angle lens combo set up on land as well as water- to give me an idea of corner sharpness??

If so- that would be even better/easier to do- and is a bit more eco-friendly than filling a bath tub with precious water.

Sorry to confuse you. You need to have the dome in the water to test the corners.

You don't need a tank if you don't want to upset the pool folks. Snorkel is helpful but not absolutely required. Just show up at the pool and shoot in the shallow end.

Steve