should I get 5d mkii aquatica housing?

How did you determine the back plate is sealing?  Did you use a vacuum test?  It is flat contact o-ring and the back plate needs to be able to move in to seal properly so it can compress the o-ring.  It's your housing and expensive L- Lens but I would not dive with it like that.

BTW the reason for the correct extension is to get the best optical quality from the lens - it seems counter intuitive to me to want to use a lens because of the optical quality but compromise on the dome placement.

good question, Chris

No I have not done a vacuum test but the gap with the lens and without a lens is visually the same 

And yes I would not want to lose the camera and lens - I'll just have to wait till backscatter or blue waters get the ports back in stock

A little frustrating that they both list the ports as in stock but don't really have stock

Generally speaking, how far back should a lens be from the dome or flat port?

Thanks for your and everyone's help here.

9 hours ago, hedonist222 said:

good question, Chris

No I have not done a vacuum test but the gap with the lens and without a lens is visually the same 

And yes I would not want to lose the camera and lens - I'll just have to wait till backscatter or blue waters get the ports back in stock

A little frustrating that they both list the ports as in stock but don't really have stock

Generally speaking, how far back should a lens be from the dome or flat port?

 

Thanks for your and everyone's help here.

It's quite variable, you want the entrance pupil to coincide with the centre of the radius of curvature of the dome.  You can measure the nodal point your self or even estimate by looking at the apparent location of the aperture blades.  Once you have that you can compare it to nodal points of other lenses here:https://wiki.panotools.org/Entrance_Pupil_Database

If yu find a lens on that port chart with the same nodal point distance  you need the same extension.  You also need to know the radius of curvature of your port it - this can be calculated if the port is not a hemisphere- or if it is, then radius is half diameter.  Formulafor radius is here:  https://sciencing.com/radius-arc-7846775.html

Many thanks but that is too technical for me, Chris.

Port charts don't mention nodal distances.

Just the port and compatible lenses.

45 minutes ago, hedonist222 said:

Many thanks but that is too technical for me, Chris.

Port charts don't mention nodal distances.

Just the port and compatible lenses.

that's right they don't, but the chart I linked does - if you can approximate where the entrance pupil lies and measure the distance from th lens mount to that point - you can estimate what extension is required.  Look down your lens and place your finger on the lens barrel at the depth it looks like the aperture blades are located.  Measure from the lens mount to this point .  This will get you in the ball park for the correct extension.  You just look for a lens with the same nodal point distance that is also in the Aquatica lens chart and use the extension recommended for that lens.

I will likely be selling my 5D mk II housing soon. Just upgraded to the R5 topside and am transitioning the underwater gear now. Probably won’t sell my dome port, but will be offering up the macro port, the straight viewfinder and some extension rings.

Two must have lenses…a 15mm fisheye (sigma or canon ) and the 100mm macro. All the other lenses you listed have trade offs in image quality behind domes less than 9 inches or don’t focus close enough (remember that closer is better underwater)

I haven’t really thought about price yet, but can probably set you up well if you are interested.


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2 hours ago, chidiver said:

Two must have lenses…a 15mm fisheye (sigma or canon ) and the 100mm macro. All the other lenses you listed have trade offs in image quality behind domes less than 9 inches or don’t focus close enough (remember that closer is better underwater)

Looking at the port chart, the 17-40 would probably be OK in an 8"dome if you stop down to around f13 or so, the 24-105 requires a +3 diopter as it doesn't focus close enough and a longer extension than the 17-40.    If you are housing say the 17-40 you could purchase the extension for that lens to try out with your 35mm f1.4 if you are determined to try to use it UW.

8 hours ago, ChrisRoss said:

Looking at the port chart, the 17-40 would probably be OK in an 8"dome if you stop down to around f13 or so, the 24-105 requires a +3 diopter as it doesn't focus close enough and a longer extension than the 17-40.    If you are housing say the 17-40 you could purchase the extension for that lens to try out with your 35mm f1.4 if you are determined to try to use it UW.

Thanks for your advice

I remain determined

I picked up the:

Canon EF 24mm f/1.4L II port #48456

And the 

Canon EF 17-40mm F/4L USM port# 48458

The 35 1.4 dimensions are almost identical to the 24 1.4

I wish someone could or would look up the 35 1.4 focusing thing - I tried but struggled

Willing to barter for helping with accounting

According to the database the entrance pupil for the 17-40 is located approx 70mm from the lens flange, measure 70mm from the lens flange and mark that on the lens.  Place your finger there and look into the front of the lens - it may help to mount the lens and stop down the aperture.  That should appear to at the same depth in the lens as the mark, placing your finger on the mark should help visualise that. 

Next do the same with the 35mm f1.4 place your finger on the barrel outside at the depth where the aperture iris appears to be, mark it and measure how far up from the lens flange the mark is.  From that distance I can estimate approximately what sort of extension you need.  _ it's only an approximation mind you but it's better than nothing. 

Unfortunately you need the lens in your hand to estimate where the pupil is.  If it's the same dimension as the 24mm f1.4 I would guess it would need similar extension or slightly less.

The alternative is to just try the 48456 extension and see how the results look.

4 minutes ago, ChrisRoss said:

According to the database the entrance pupil for the 17-40 is located approx 70mm from the lens flange, measure 70mm from the lens flange and mark that on the lens.  Place your finger there and look into the front of the lens - it may help to mount the lens and stop down the aperture.  That should appear to at the same depth in the lens as the mark, placing your finger on the mark should help visualise that. 

Next do the same with the 35mm f1.4 place your finger on the barrel outside at the depth where the aperture iris appears to be, mark it and measure how far up from the lens flange the mark is.  From that distance I can estimate approximately what sort of extension you need.  _ it's only an approximation mind you but it's better than nothing. 

Unfortunately you need the lens in your hand to estimate where the pupil is.  If it's the same dimension as the 24mm f1.4 I would guess it would need similar extension or slightly less.

The alternative is to just try the 48456 extension and see how the results look.

 

Yes the 48456 is for the 24 1.4 L

It looks to be between 5 and 7 cm away from flange.

I'm sorry if I'm burdening with my questions, why would I need to stop down?

I'm certain there are optical and physical reasons, but in layman's terms?

Thank you.

When you stop down the lens for this purpose - you can see th diaphragm close so you are certain you are looking at the right spot. - it's not always obvious.

1 hour ago, ChrisRoss said:

When you stop down the lens for this purpose - you can see th diaphragm close so you are certain you are looking at the right spot. - it's not always obvious.

 

I meant why stop down during shooting - but I see that was already addressed in this thread.

I measured from flange of 35 f/1.4 L to where the diaphragm appears to be:  about 50mm to 70mm  

9 hours ago, hedonist222 said:

I meant why stop down during shooting - but I see that was already addressed in this thread.

I measured from flange of 35 f/1.4 L to where the diaphragm appears to be:  about 50mm to 70mm  

 

I would suggest trying it with your extension for the 24mm, looking at the measurements, the 17-40 extension would be too long I think.   The 35mm will be less fussy about stopping down as the field of view is smaller, but I'd still shoot at f8 at a guess.  If you get a chance in a pool take shots of the pool wall at f5.6/8/11 to see how it performs - using a pool allows you to get parallel to the wall and have even detail of the tiles out to the corner so you can judge where you are happy with corner performance.  You could probably also do it shooting straight down onto sand - take the shots at about 0.5m away. 

In demonstration of my gratitude to you all, here are are few JPGs straight out the 5d mkii with the 35 L on.

48456 port and 8" acrylic dome.

f/4 1/60 and 1/100 and ISO 100

They look ok to me?

Those are taken in air. With air on both sides of the glass, it does not modify the image aside from some very minor loss of sharpness and potential flare. It's when you place it underwater that different refraction indices come into play, and the dome starts acting as an additional lens element. If you google 'dome port theory', you'll find plenty of articles explaining the effect.

38 minutes ago, Barmaglot said:

Those are taken in air. With air on both sides of the glass, it does not modify the image aside from some very minor loss of sharpness and potential flare. It's when you place it underwater that different refraction indices come into play, and the dome starts acting as an additional lens element. If you google 'dome port theory', you'll find plenty of articles explaining the effect.

thanks for the input

till I get to try it underwater, what are you suggesting I may find out underwater?

If the lens front element is right up against the port glass, I would expect a reduced field of view, smeared corners and some  pincushioning. Being this close to the glass, the effect should be close to a flat port. Here is a 45mm lens (16-50mm @ 30mm on APS-C) shooting through a dome (properly placed near its nodal point), and here is the same lens shooting through flat glass. The effect is more pronounced at wider FoVs, as you can see here for 16mm (24mm-equivalent) through dome, and here through flat glass. For a 35mm lens on full-frame, I would expect the distortion to be somewhere between these two examples. Just for the reference, this is the amount of distortion that a 15mm-equivalent (10mm on APS-C) lens experiences behind a flat glass port.

The 5D Mk II is a great camera, but I think you really need to rethink your lens options. As others have pointed out, optics behave significantly differently underwater and many (very good) optics simply do not provide acceptable image quality when used behind a dome port and in the water.

Granted, I have no personal experience of using the 35mm behind  port, but given that no one else in this community has either, I think it is unlikely to work. It really is far too narrow to be a useful focal length underwater anyway. 

Saying that, if you want to go to the time, expense and effort of testing it underwater, I'm sure we will all be very happy to see your results

21 hours ago, Barmaglot said:

If the lens front element is right up against the port glass, I would expect a reduced field of view, smeared corners and some  pincushioning. Being this close to the glass, the effect should be close to a flat port. Here is a 45mm lens (16-50mm @ 30mm on APS-C) shooting through a dome (properly placed near its nodal point), and here is the same lens shooting through flat glass. The effect is more pronounced at wider FoVs, as you can see here for 16mm (24mm-equivalent) through dome, and here through flat glass. For a 35mm lens on full-frame, I would expect the distortion to be somewhere between these two examples. Just for the reference, this is the amount of distortion that a 15mm-equivalent (10mm on APS-C) lens experiences behind a flat glass port.

Thank you - I need a bit of time to digest this.

18 hours ago, adamhanlon said:

The 5D Mk II is a great camera, but I think you really need to rethink your lens options. As others have pointed out, optics behave significantly differently underwater and many (very good) optics simply do not provide acceptable image quality when used behind a dome port and in the water.

Granted, I have no personal experience of using the 35mm behind  port, but given that no one else in this community has either, I think it is unlikely to work. It really is far too narrow to be a useful focal length underwater anyway. 

Saying that, if you want to go to the time, expense and effort of testing it underwater, I'm sure we will all be very happy to see your results

Technically speaking, the 35 is about 99% of the 24 L.

The port extension  was designed for the 24L.

Size-wise, the 24 L and 35L are almost identical.

But you're right. I am unsure and would like to find out.

Worst case scenario, I either get a 24mm or sell the extension ring.

Photographs in a weeks time