Macro lens behind Dome Port?

Ok, I know that you "should" use a dome port with wide angle lenses and a flat port with macro. Could somebody tell me why? What would be the effect on using a macro lens (let's say 50mm or 60mm) behind a dome port?

Also, what macro lens would you recommend (I have a Canon 300D with Aquatica housing)?

Thanks

Hi!

I will try to give you a simple answer to your question:

A flat port magnifies a dome port doesn't.

Actually the dome port works as a kind of negative lens to compensate the magnifying effect when light travels from water to air.

For physical reasons I don't want to explain (as I have to read it up myself again), you should use a dome port when shooting wider than say 35mm as the quality off center decreases and the dome port compensates for that.

Also when shooting wide angle you don't want a magnifying effect as you want to go wide. Therefore you should use a dome port.

Flat port is obviously easier and therefore cheaper to produce and a magnifying effect is probably seen as an advantage when shooting macro.

I need to post a question as well:

I would like to buy the canon 100mm macro.

I think that the 50mm will probably not be long enough for what I want, but on the other hand I'm not sure if the 100mm might eventually bee too long.

As I want to travel light, I think about using it behind a dome-port as well. Therefore I would only need one port (probably with extension ring) and don't need to carry a second flat port.

As the dome port doesn't magnify the combination should be longer than a 50mm macro behind a flat port but still shorter than 100mm+flat port.

Could anyone tell me, if this makes sense or not?

Is there any trade-off in image quality when shooting a macro lens behind a dome port?

Regards

Robert

Hi!

Is there any trade-off in image quality when shooting a macro lens behind a dome port?

If I remember it correctly, a dome should, ideally, be a sphere with the lenses nodal point as the center. The glass should be a segment of this sphere according to the viewing angle of the lens.

If the dome doesn't match the lens you will experience bad image quality (at least) in the corners. You may try several combinations in a bath tub to find out if it works.

Print a test image (like the ones used for lens testing) and seal it. A simple grid will do it too. You might even use a plasic ruler or similar. Take some pictures in the bath tub. That's all you need to find out.

Helge ;-)=)

Actually a dome is best for macro as well as wide angle. You lose the magnification effect of a flat port and they are usually larger and more expensive but they limit Chromatic and other aberrations they tend to occur more with a flat port than a dome.

Hi!

 

I would like to buy the canon 100mm macro.

 

I think that the 50mm will probably not be long enough for what I want, but on the other hand I'm not sure if the 100mm might eventually bee too long.

 

As I want to travel light, I think about using it behind a dome-port as well. Therefore I would only need one port (probably with extension ring) and don't need to carry a second flat port.

As the dome port doesn't magnify the combination should be longer than a 50mm macro behind a flat port but still shorter than 100mm+flat port.

 

Could anyone tell me, if this makes sense or not?

Robert, thanks for your answer. I have ONE MORE question: I have the kit lens (18-55mm). Does it make any sense in buying a 50mm lens if the kit lens goes to 55mm? Should I instead look at a 60mm or 100mm? Similar to your case, the idea is to travel with one single port (as long it does not sacrifice quality too much).

Neither lens will do 1:1 macro, but the 50mm 'macro' will do 1:2 which should be a lot better magnification than your kit lens. Optically, the 50mm macro will be way better. I'd use the 18-55 as a general use lens, mainly for wide angle, and use either the 50mm or 100mm macros for the purpase they're designed ie close-ups.

Many people say the 50mm is easier to use if you're starting out. I've only used a 90mm macro underwater (the Tamron), which worked fine. Get the 100mm if you want to shoot 1:1.

a dome should, ideally, be a sphere with the lenses nodal point as the center. The glass should be a segment of this sphere according to the viewing angle of the lens.

If the dome doesn't match the lens you will experience bad image quality (at least) in the corners. You may try several combinations in a bath tub to find out if it works.

Hi,

this is correct but the center of perspective is not the nodal point (as often stated). nowadays (wideangle)lenses are built retrofocus. You can consider these lenses as a base lens with a built in conversion lens. Otherwise 15mm focal length would not be possible without hitting the mirror.

The center of perspective is located with the lens entrance pupil. the two nodal points (entry and exit points) of the base lens are located behind the entrance pupil.

For macro lens behind a dome it could be important that a dome port places a close virtual image in front of the dome where the lens has to focus on. So possible close focus may be reduced depending on the lens and dome used.

regards,

Julian

Get the 100mm if you want to shoot 1:1

Or get the Sigma 50mm, which shoots 1:1.

Also, the 100mm macro is a much more specialized lens, by which I mean you're going to be much more limited in what you can shoot with the 100mm than with a 1:1 50mm. This is why many people say that the 50mm is easier to use to start out, it's a more versatile lens for capturing macro through fish portraits.

That being said, I have a 17-40L and a 100mm macro (both canon), and no 50mm.

Just my $0.02

Tom

Actually a dome is best for macro as well as wide angle. You lose the magnification effect of a flat port and they are usually larger and more expensive but they limit Chromatic and other aberrations they tend to occur more with a flat port than a dome.

Yes, and I think you could say that flat ports are used with macro because they are so easy. Chromatic aberration that results from using a flat port is quite easy to see and should be compensated for. Domes are tricky to get right and are only "essential" for wide angle. I've used a dome with the 60mm and 105mm with great success (although I generally don't use those lenses anymore). Domes require closer focus somewhat negating the advantage of a macro lens.

That being said, I have a 17-40L and a 100mm macro (both canon), and no 50mm.

I actually had the camera salesman talk me OUT of getting the 50mm macro lens when I bought my DRebel, since the kit lens focuses fairly closely. You get around 1:3.5 with the kit lens at 55mm, you get 1:2 with the Canon 50mm macro, and you get 1:1 with the Sigma 50mm or the Canon 100mm.

As I understand it, beto, this means that you have roughly the same angle of coverage (focal length) between the kit lens at 55mm and the 50mm macros, but you can put the lens closer to the subject with the Canon 50mm macro lens (9.6 inches) than with the kit lens (11 inches) - so your resulting apparent image of the subject is nearly twice as "zoomed in". The Sigma 50mm or the Canon 100mm macro lens can get twice as "zoomed in" an image as the Canon 50mm - but with the Sigma, you have to place the lens 7.4 inches from the subject, while the 100mm would be placed at 12 inches. (That's kinda close for me - I usually spook the fish when I'm that close.) Note these are all calculations for in the air, without accounting for flat port magnification effect. The 50mm lens are both around $250-300, the Canon 100mm is around $550-600.

Personally, I'm going to keep working with the kit lens for a while and then get a 100mm macro. The other benefit is with the kit lens, I can zoom to wide-angle on the same dive - with any of these macro lenses, you have to choose to stay at the same focal length for the whole dive, and I'm not that good at planning my photography subjects yet. Of course, here in Seattle, most of the photography ends up being macro due to visibility anyway.

Wow, so it looks like I just got rid of one port. Maybe I shouldn't have bought the flat port after all. Can anyone give me a good reason why I should use my 60mm Nikon lens with the Ikelite 5505 flat port instead of the 5503.50 dome that I am already bringing along for my 12-24mm anyway?

What about diopters? The 60mm focuses down to 8 3/4" which is less than the 12in cutoff that Herbko recommends for 6" domes (I think this comes from 2x diameter). But what about the 105mm? It only focuses down to 1 foot. I'm not sure if this is 12in or 12.something in the Nikon specs say only 1 foot)--at any rate this is close. The Sigma 105mm states 12.1 in which is also close.

Also, Ikelite states that the 5503.50 dome can be used with the Nikon 60mm but doesn't list any dome that can be used with the 105mm. Why is this? The sigma 105mm should fit--website states that it is 3.7" fully extended whereas the 5503.50 is made for lenses less than 4" in length. The Nikon 105mm is 4.1" (not sure if this is extended or not) which seems close enough to 4".

Does anyone have an opinion of the Nikon vs Sigma 105mm? The new Sigma optimized for digital looks sweet and is about 1/2-2/3 the cost of the Nikon, while being more compact.

This in not a good way to save a hundred bux.

The reason for using a dome for macro is image quality, it's not an excuse to leave one port at home...

Cheers

James

a second dome for the macro lens?

The reason a dome isn't listed for the 105mm is likely that no one has requested it so Ike never tested it. I've used a dome with that lens and it works well except that a +3 diopter must be used with my setup.

The dome must be matched properly to the macro lens just as it does for a wide angle lens. Fortunately, macro is usually shot with small apertures that would be more forgiving of errors in this regard.

a second dome for the macro lens?

If the second dome is matched better to the macro lens then yes.

I don't mean to sound cynical but look at it this way. You're more than likely spending a few thousand $$ to get a DSLR housed between the camera, lenses, housing and ports, even if you're getting the cheapest housing available. Don't try to save a little bit of money or weight by skimping on ports, they have a direct and significant effect on image quality.

If you want to cut weight and money, house a P&S, or limit the number of lenses you start out with. Truth is, each lens you house is going to take a lot of practice to get proficient with.

Ok, off the soapbox now...

Tom

Hi

the original quastion was if skipping the flat port and using the lens behind the WA dome would make sense.

I don't think it makes sense. Better the dome for the WA and the flat port for the macro lens. So here I agree that money saving on a flatport doesn't make sense.

But I was just wondering about the hint to replace the flatport with another dome port for the macro lens only.

Usually with a FOV less equiv. 35mm focal length a dome really is not necessarry and doesn't gain anything.

A 50mm Macro lens on the mentioned camera gives a FOV equiv. 80mm focal length.

So why a dome for the less than 25° FOV ?

I don't want to ride on this topic but I really just didn't get it because I have seen no housing manufacture selling domes for macro lenses so far, just for WA (35mm and below).

regards,

Julian

Well, I don't think dome ports are typically recommended, but you can get Ikelite ports that look like they would physically fit the macro lenses - in fact, Ikelite even lists the appropriate dome port for the Canon 50mm macro lens on their port chart: http://www.ikelite.com/web_pages/2port_canon.html.

I do have the same question, though - should I get a flat port or a dome port for the macro lens? If expense is the issue, that seems silly - if memory serves, the dome vs flat port cost difference is <$100 for the Ikelite ports. If magnification is the only benefit of the flat port over the dome port, well, 1:1 magnification seems like it would be plenty to me if the dome port has better image quality - but it seems like a flat port would be easier to make with higher quality than a dome port.

Interesting concept re: the macro behind the dome port, but I think I'll keep it simple and plan on using a flat port for now.

A quick measurement of my Canon-mount Tamron SP AF 1:1 macro shows that it extends from 9.5cm to 15cm while focusing. I'm guessing that it would be hard to find a dome port to fit over that.

Do the rest of the Canon-mount macros change in length when focusing like this?

I'm a bit worried about the effect of having the front element of the lens 10cm+ from the glass of the port. Does this make a difference?

The Tamron's hard to find port information on, and although it's optically a very sweet lens I'm thinking of replacing it with the Canon 100mm, especially since I saw the manual-focus Ikelite port on another thread.

<edit> This is slightly more than an academic discussion for me now as I've decided to buy the 5503.50 dome for my 17-40L, which is the port mentioned above that Ike recommends for the Canon 50mm macro. For $239 dollars for the 50mm, it's got to be tempting to give it a try under the dome port.