Verification on angle of view

Hi Guys,

After speaking with the Pakman, I need clarification on an issue that has just come to light during an experiment with a new lens. I'm doing extensive homework, behind the scenes, before handing over the cash on a new lens. I am looking at the Sigma 18-50mm macro HSM lens and will probably ask it to do things, of which I am sure, that it was not intended to do... , to be more specific, I will be using the 'longer' end of the zoom for super macro and the 'shorter' end for the occasional portrait of fishies...

So far I have found out that the 18-50mm 'becomes' a 27-75mm when used on a Nikon DSLR(1.5 conversion factor) and used behind a dome port. Now when used behind a flat port, this lens then becomes a 37.5-112.5mm macro zoom. Now remember that these are mathematical computations to the origional 18-50mm lens.

When the 18-50mm lens starts out, it has an angle of view 76.5 degrees at the 18mm setting.

What happens to this angle of view when it is subjected to the above mathematical computations?

A Sigma lens with constant 2.8 aperture and approx., 37mm focal length

in a normal wide zoom, before the computations, has an angle of view of approx., 55 degrees. Will this be the same, approximately, as the 18mm after computations or are there other factors that have to be taken into account?

The reason for these queries is within regard to vignetting. The lens is to be housed behind a flat port with a front 'window' of 100mm, and an overall length suitable for the maximum length of the zoomed out lens.

I was hoping that the resulting images would not show vignetting at the 18mm(37.5mm) end of the zoom??

Anyone have any clue as to what I'm talking about...

Bruce...

Hi Bruce

I'll give it a go!

Your 18mm lens will have a certain angle of view on full frame 35mm format (36mm x 24mm diagonal) but on Nikon's DX format you are only utilising a part of this image so effectively you are using a reduced field of view (forget 'equivalent' focal lengths - think about the angle subtended on a DX format diagonal). This means that you have a specific field of view 'seen' by the lens on DX format. The lens/format will see this field of view even behind a flat port - its the refraction through the port 'glass' which further reduces the effective field of view. So to answer your question (?) I think that you need to work out what length flat port you will need with the reduced field of view due ONLY to the DX format. Does this make sense/help?

Hi Bruce,

I don't want to confuse you even further but their is no "crop" for the Sigma 18 to 50 mm F/2.8 EX DC macro HSM because the lens was not designed to work on a 35 mm camera to begin with. Just as their is no crop for a

medium format lens. A 6 X 7 medium format 50 mm lens has an angle of view of 81 degrees, a 35 mm 50 has a 46 degree AOV, a Nikon DX Sigma 50 mm has a 31.7 degree AOV and a Olympus 4/3 50 mm lens has a 24 degree AOV they are all made to work "full frame" not reduced or expanded from some other format.

If it helps for you to compare the AOV to lenses made for 35 mm that is understandable for some but according to Sigma this lens has an AOV of 76.5 to 31.7 which is what it is.

A 35 mm lens of 18 to 50 mm would have an AOV of 100 degrees to 46 degrees because that is what it is.

The issue of dome port or flat port remains constant regardless of the format and refraction with the flat port will further reduce the angle of view of any lens.

Phil Rudin

Thanks Guys,

You make it sound so simple. I have had no formal training in this sort of thing and as such it is quite confusing at times.

Phil, you point out an obvious oversite that makes me look rediculously stupid. I hadn't taken into account the fact that the lens was in fact made for the AP-S sensor...

Luckily for me, I asked these questions before I laid out the cash for a lens...

Thanks for your help fellas...

Oh well, back to the drawing board...

Bruce...

Oh well, back to the drawing board...

Steve

Hi Stevie,

Nikkor used to make a 70-180mm zoom micro lens for film or full frame cameras. Apart from a slow AF system, this lens was supposed to be the 'ducks guts'... B)

These lenses are no longer made and are not suitable for APS-C sized sensors.

I use the Nikon D70S camera in a Nexus housing.

What I want from a lens is to perform/work at the same focal lengths as the 'said' Nikkor.

My needs are 95% around the 90-130mm focal range but I want the choice of being able to change the zoom for an occasional 'fishie' portrait...

The les has to be able to focus closely, with or without diopters, and have decent magnification, as well as retaining a workable depth of field for all zoom focal lengths...

It's as easy as that my friend. Any advice... , that's printable...

Bruce...

Hi Bruce,

Just for fun I went looking around the Nexus and Sea & Sea sites to take a look at what they make ports for. I will remind you I'm shooting a Canon and have no business playing in the Nikon world. But since you asked I see a couple of things that you might want to checkout. Nexus makes a port for the 28-105mm f3.5-4.5D AF 74-23. It takes a 62mm filter, close focus 1.7 feet will only do 1:3 macro and it needs a diopter. The other one is right up your alley. The 70-180mm f4.5-5.6D AF ED. (Which I thought they quite making years ago) Takes a 62mm filter, focuses down to 14.6 inch and will do macro down to 1:1.3. I think this is the Big daddy lens and port you were wishing for. You'd look great chasing stuff around the reef with this baby. They show an adapter for the D70 on the Nexus America site. Of course you might need a lift bag to keep it off the bottom but hey, go for it. Sea & Sea calls out a port for the Nikkor 18-70mm, is that more what your looking for?

Uh, whats wrong with just hanging the 60 or the 105 off the front? Too easy?

Steve

Bruce,

About as close as you are going to get to that lens in the DX format is the 18 to 135 mm F/ 3.5 to 5.6 G IF-ED. This lens is "optimized" for the DX-format, no crop in other words, I.E. made for DX only.

Its zoom range is 76 to 12 degrees, with a minimum focus distance of 1.5 feet (46 cm) and a 1:4.1 magnification.

The 5.6 is slow on the long end for AF to 1:4.1 and the wide end will not work well under a flat port.

I agree with Steve, if you want a lens to do macro pick a macro lens. You can add extension tubes, tele converters and diopters if you want to change the angle of view of the lens and still get much better AF performance.

Phil Rudin

I have this lens.....18-50 F2.8 MAcro HSM right? I got it on my D300.

The guys are right.....it isn't quite wide enough for proper WA shots and although will focus VERY close (and no diopters needed behind a done), you will find yourself wishing for a full on macro lens...

However, I have this lens soely because I fear not having the right lens for the dive. It will do fish portraits brilliantly and still allow me some closeups which may require a little cropping....It works well as a shark lens too.

I have it behind an 8inch dome port and Sea & Sea's SX extension ring. A bigger dome port would of course be better....

Hi Phil,

I have the 60mm and the 105mm micro's with Nexus CL 'wet' diopters and 1.4 teleconverter.

I usually have the 60mm with teleconverter hooked up to the camera and the wet diopter tied up front for that little bit extra when I need it. Quite often I will come across a nice portrait oportunity with a jelly fish of some 'other' nice fish and find that I'm unable to get "the" shot and have to end up taking partial images.

Then at the other end of the scale, I will quite often come across particular nudibranchs that are about 12mm in length and again I cant get "the" shot that I want and have to crop the images afterwards.

I was really hoping to be able to have the 'options' covered. The 'options' are not THE reason for the dive, but they tend to crop up once or twice during every dive... very frustrating.

Bruce...

Bruce,

I feel your pain but the photographers I have known who used the Nikkor 70 to 180 mm macro on their film cameras were not all that happy with lens in or out of the water.

I have just started using the Olympus 12 to 60 zoom in the past few months. Angle of view is 84 to 20 degrees, the lens will focus to less than nine inches, (23 cn) with magnification of about 1:2. Since it is an F/2.8 lens AF is super fast and balls on. DP Review describes the lens as "superb" and I would agree. The down side is on the macro end because you need to be very close when the lens is used behind a dome port. If I was only allowed one lens on a travel assignment for both above and under water this would be it. I use it behind the 170 mm Olympus dome port with the extension tube for the 7 to 14 zoom, a custom gear and my E-3 in a Nexus housing.

I guess we just need to start carrying two or three cameras on every dive to cover the entire range.

Phil

Just to be clear - the 70-180 was not "made" for FF or film cameras - it worked GREAT on cropped sensor cameras too. I used to have one when I shot Nikon and I loved it.

Cheers

James

James,

No one said the lens was "made" for film cameras, only that the shooters I know who used this lens used it on film cameras.

The lens was introduced in 1997 and discontinued in 2004. At the time it was introduced AF was not as good as it is now and that may account for the mixed reviews from my friends.

The fact that this lens works on a cropped sensor has nothing to do with getting Bruce into angle of view range of this lens on 35 mm.

Bruce, if you like the 70 to 180 mm macro focal range on a 35 mm film or digital sensor you could always get a new Nikon D3 and the new Nexus housing that is coming.

Phil Rudin

Well yes, actually - Bruce did say that 8 posts up. But that's not important - what's important is that the lens is good on film cameras and SUPERB on digital cameras, because w/ the 1.5x crop it does greater than 1:1 (35mm equivalent).

Even though the lens doesn't quite fit into the range of subjects Bruce is interested in, it gets really close. The lens is varifocal, so that it is actually a 90mm lens at its longest at close focus.

Craig, myself, Larry Jackson, and a few other digital folks use this lens, and I know Larry has made the transition from film to digital and still uses the lens w/ the Nexus multiport. But if Bruce wants something a bit wider, I suggest having a chat w/ Stu Sy (Scubastu on here) who is very happy with the Canon 28-105 on his APS-C sensor camera. Perhaps Nikon makes an equivalent lens?

Cheers

James

C'mon fellas...

I hate to see nice blokes goin' at it because of my dumb questions...

James, if I could find a 70-180mm Nikkor, I would be stoked...

I've advertised and even emailed the local Oz distributor for Nikon to see if they had any refurbished or s/h lenses hanging around? The lazy pricks didn't even bother to answer...

James, I don't understand what you mean when you say that the 70-180mm micro was a "vari something" lens and its only 90mm at the wide end...how does this work...

This would make the 70-180mm the same at the wide end as my 'normal' 60mm micro, as this supposedly equates to 90mm when put on a DSLR due to the cropping factor???

If this is true, then I need to find myself a Nikkor 70-180mm micro very soon. THIS WOULD BE GREAT...

Geez, I think I'm getting one of them achy, head aching things when me head hurts from aching...

Bruce,,,

Dear Santa, can you please ask your elves to be on the lookout for...