Question On UV Filters (1 Viewer)

I have recently purchased a Swarovski ATS 80 HD scope and was considering putting a UV filter on it, mainly as protection for the objective lens, but since reading some of the posts on BirdForum regarding UV filters, now I’m not so sure.

I used to put UV filters (or sometimes a 1A filter which I found imparted a faint pink tinge to clouds) on all my film SLR lenses as a matter of course. Back then, and this is going back quite a few years, all the UV filters I bought were completely clear and, as far as I could tell, they gave no colour cast to the photo nor degraded the image (or altered the exposure) in any way.

What they did do, however, was markedly reduce the presence of mist, smoke, dust, pollution, etc in the resulting image. The reason for this was, if I understood correctly, was that the colour transparency film I was using (and I assume, most other colour films as well) were sensitive to UV light and this light was scattered by the tiny particles floating around in the air. (I think this is similar to the effect that causes the sky to be blue.) In most cases the use of the filter spoilt the effect of the mist on the lake or the smoke rising from the camp-fire, etc, as it was greatly reduced, or eliminated.

The question I have - I’ve finally got there - is; are the sensors in digital cameras also sensitive to UV light? If they are, then I would have thought it would be an advantage to use a filter when digiscoping as, by its very nature, you are looking through a significant chunk of atmosphere that will nearly always contain a quantity of light scattering particles. If this haze could be eliminated by use of a filter, then clearer, sharper, more vibrant photos should result.

I would be interested to hear your thoughts and experiences on this matter.

Answered My Own Question

Having had no replies to my query after a week, I decided to do some searching elsewhere on the web and finally found the answer at http://dpfwiw.com/

For those that are interested, and it seems quite possible that there may be none, |=)| I reproduce some of what I found below:

UV sensitivity seems to vary from one digital camera to the next, but most digital cameras seem to be substantially less UV-sensitive than film. In fact few digital cameras are UV-sensitive enough to reap a noticeable optical benefit from UV filtration, even in the most extreme UV conditions, and seldom deliver a benefit worth the added risk of flare. A good quality multi-coated neutral UV filter, however, is as good a choice as any for a lens protector if you feel compelled to use one, but don't expect to see much of a benefit in your digital images.

Cameras prone to an artefact known as purple fringing are notable exceptions. Fringing turns out to be at least partially suppressible with a UV cut filter in such cameras.

Protective Filter pros are as follows:

• Filters are generally a lot less expensive than lenses.

• Which would you rather replace, a screw-on filter or a built-in zoom lens?

• Optically, quality multi-coated UV filters have little downside on a properly shaded lens.

• UV filters generally require no exposure compensation.

• Not so obvious is the potential for irreversible salt spray damage to optical coatings, especially when the salt is allowed to remain on the glass for some time. Consider an uncoated plain or UV filter for that day at the beach, especially if the surf's up and the wind is onshore.

Other posts on BirdForum have talked about the colour-cast that some “UV” filters imparted to their photos. The answer to that is that they are a special type of UV filter known as a Haze Filter:

Much of the haze seen in visible light film photographs results from the scattering of UV-A by air molecules, water droplets and particulates. Haze filters provide stronger UV-A filtration than most of the commonly used neutral UV filters, but at a price: They also block some visible blue and impart a variably conspicuous yellow cast in the process.
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Thanks for coming back with an answer, Avocet. I'm surprised that no-one on BF noticed or replied to your query, I think that's unusual.

If you feel your Post is being 'ignored' or lost in the volume of messages on BF, the simplest method of bringing it back 'into view' is to 'bump' it occasionally.

If I've read the reply right, a good quality UV filter can cut down CA (Chromatic Aberration - purple fringing) on a digital camera that is prone to it - but ensure this is used with a lens hood/shade to minimise the flare? That sounds like a very good reason to use a UV filter/shade combination.

Cheers,

Andy.

Just to echo Andrew's observations - a lack of response should never be taken personally, because it generally means you're breaking new ground!



Now that I've read your response to yourself () I can see a lot of benefit in getting hold of a filter for my scope too, so many thanks for that.

Thanks Andy and Keith for your replies and advice.

On the basis of what I’ve found out, I will buy a UV filter and give it a try to see if it helps the purple fringing problem from which some of my photos have suffered in the past. I will take a few test comparison shots and report the results back here in due course.

It appears that purple fringing, which only seems to affect digital cameras, is not typical chromatic aberration. The dpfwiw explanation put it this way:

Whatever the cause, if UV filters help reduce or eliminate the problem, I’ll be happy. It sounds as though Hoya Super HMC filters may be the way to go - they have 12 coatings (and a price to match) and transmit 99.7% of the available light according to Hoya's advertising. This should make them virtually invisible to the camera.

My problem now is that Swarovski, for reasons known only to themselves, have the filter thread on the outboard end of the slide-out built-in lens hood - the worst possible position if flare is to be avoided. Don’t know how I’m going to overcome this one yet. :h?:

Recurvirostra said:

My problem now is that Swarovski, for reasons known only to themselves, have the filter thread on the outboard end of the slide-out built-in lens hood - the worst possible position if flare is to be avoided. Don’t know how I’m going to overcome this one yet. :h?:

Click to expand...

Hmm .. , the only resolution to this that I can think of offhand, is to use a screw-in lenshood to add to the filter - it should be fairly straightforward to get one to suit - but you'll need to ensure that both filter and hood don't become detached together and lost in the field!

good luck with it

Andy.

FWIW a few points. Chromatic aberration, especially lateral CA, can be purple, and a Nikon 28mm F2.8 AFD lens I once owned suffered from purplies in the out of focus highlights among other faults which is one reason I sold it and bought the manual focus version.

Just in case you're not aware, several manufacturers produce clear 'filters' that protect the front element without adding a colour cast. I have a Canon one on my Leica scope but Nikon also make them, but at a higher price (in the UK anyway). I've no doubt they introduce some (insignificant?) image degradation but I consider that a small price to pay for the protection provided.

Some info on UV and digital cameras is to be found on Bjorn Rorslett's site. As mentioned, there is some filtering of near UV, possibly by the filter that sits in front of the sensor, or possibly the sensor itself is less sensitive to UV than film. Far UV is of course filtered by glass! Another place to find info is www.photo.net. It's a bit geeky, but then again blessed are the geeks.

Leif

That's a great idea Andy. I had completely forgotten about the thread in front of the filter in my quest to find the most complex, expensive and time consuming solution. |:$|

And thanks too for bringing the photo.net site to my attention Leif. There is a mass of good information there. I think I will stick with the UV filter rather than the clear protective ones at this stage, in the hope that it has a positive effect on the purple-fringing problem. It shouldn't degrade the image any more than the clear filter so the only downside is the (I imagine) extra expense. ||

Hi John!

Nice to see you here. (Or should that be nice to see me here? I've not popped in much of late.)

I actually have a UV filter for the ATS-80, somewhere around the place. I bought it several years ago, essentially as a protector for the scope in case of dropping it or bumping it against a rock or something, but soon stopped using it. I can't remember why I stopped using it, but I think it must have been because of the silly mounting location that Andy mentioned.

Presumably, it's still around here.

Somewhere .....

sigh

By the way, I think you can be fairly confident that the source of the purple fringing is the camera lens. (Unless maybe you are being ultra-fussy, which I doubt.) I have rarely had any problems with it using either of my ATS80 HDs, and any of my three cameras (2 Coolpix 4500s and a Canon A95). But that may be because I've become quite fanatical about always shooting down-sun or at least cross-sun wherever possible, and so not put myself into a situation where it is likely too often.

I think I used to get a little more of it with the Coolpixes than with the Canon. At least I can't remember noticing it with the A95. But maybe I just discard into-the-sun pictures rapidly threse days, whereas I used to examine every half-decent shot, hoping somehow to turn it into a masterpiece.

BTW, wouldn't having a clear or UV filter at the front of the lens shade risk introducing some of the very stray light that the shade was designed to prevent? If so, then the "cure" might be worse than the "disease". (Just a thought.)

Tony

Hi Tony,

Nice to have you back!

Since posting the above question, I have purchased a Hoya Super HMC UV(0) filter (from the USA where they are half the cost they are here). I don't think I've had any problems with purple-fringing since fitting it, so it may have helped.

You're right about the purple-fringing coming from the camera as this problem occurred occasionally pre the 'scope.

However, I now get the occasional picture where a misty halo extends around the edges of bright objects. This may well be, as you suggest, at least in part, from flare on the filter. I am looking around for a suitable lens hood to screw in front of the filter which will hopefully eliminate this problem. It may also have something to do with the photographer over-enthusiastically cranking up the zoom factor, both on the camera and the 'scope!

By the way, your Private Mailbox is full.

I don't know anything about UV filters on spotting scopes, but I know the one on my Camera does absolutely nothing except protect it from dust and damage.