Fish Eyes

[Lucy S Harte]

If you put a 15mm fish eye lens with an angle of view of 180degrees on a camera with a crop factor of 1.6 what will the actual angle of veiw be

thanks in anticipation of your responses

[robski]

Lucy

have a peek at this

http://www.bobatkins.com/photography..._fisheyes.html

[sassan]

Originally Posted by Lucy S Harte

If you put a 15mm fish eye lens with an angle of view of 180degrees on ...

Lucy;

Something is not Right here.
Most of time when I write something either gets ignored or credits goes to someone else, but I promise you if you read what follows carefully, you'll find a clear concept of what is happening with fisheye.

Are you talking of an old 35mm film camera lens or is it a Medium format lens you are referring to?

We need to have an standard size to be used as a referral for sensor or for film where image is formed on a light sensitive media. Old film camera or a full frame DSLR such as Canon 1D "s" series II & III or best of all time DSLR camera bodies, Canon 5D used to be the only full frame (I get to describe what FF is) ones and now for the very first time Nikon also has made one, D3 with full frame (Finally) of course Kodak had full frame for both Nikon and Canon lenses but the sensor was old, so to make a long story short, if you consider the size of full frame as standard i.e. 36mm x 24mm rectangle(Scroll down to "Sensor size and image quality" section), and now keep a lens at its focal distance from this frame, for eg an 8mm lens, just a littler shorter that 1cm or to say correctly 8mm from this plate, the image formed is a full circle that covers exactly one half of the field in front of the lens or to say, 180 degree (A much larger field of view compare to what both human eyes combine can look at any given time). To generate this circle that contains same field area, you must have have an 8mm lens if you are talking of 35mm film camera of FF DSLR. If smaller focal length, then same circle will have more field of view for eg Nikon once made a 6mm lens that had an area of 220 degree covered or in other word not only entire area in front of the photographer, but his head and face in addition to his legs probably up to knee.

So far we were talking only of Full Frame equivalent.
If you talk of medium format, when 120 film was used, on a 6x6 that is a common film size, the area of image would be a square 56x56mm in size. Now if you have a 15mm lens made for one such camera (Mamiya, Pentax Hasselbad) then you can have 180 degree fit to this size sensor but same lens on 35mm body (If this physically can be fit) can not produce the same degree of field coverage. So you need to tell us what exact lens you are talking about when saying 15mm with 180 coverage field.

Because the sensor of most DSLRs are smaller than FF by a factor of 1.6 or 1.5, again the same 8mm's lens circle That is larger for the area of sensor, will not fit fully on the sensor, so you can not make a 180 degree field shown (Your field is smaller by approximately x 0.625 or appx 112 degree. This would be the answer to your question if you would have a 180 degree field fisheye for 35mm format (Or in other word 8mm lens). The fact that you say 15mm lens, tells me that you are talking of medium format lens, most likely and not 35mm format. So the final field of view on APS-c sensor would be still smaller I would say approximately 60 degree. But remember I have made many speculations to answer to your question. This could be a lot easer if you could give the clear information at beginning.

Referring to Robski's referred site, that is why now Sigma has come with the solution to make a 4.5mm lens that is a true fisheye for 1.6 factor DSLRs or APS-c, and if you do the math as said above, you know why it is equivalent of 8mm lens for FF. Are these exactly equal? No but that is a different question that I have to wait and see if you are interested to have an answer for.

Hope this was clear and makes you to be able to make all the theoretical questions answered to this point.

[Lucy S Harte]

thank you for your kind responses
i will look into these later