Filters & Light Refraction


Link Posted 12/10/2005 - 13:05
....and today's silly brought to you by Mac - who's awaiting 5 eBay deliveries for his Spotmatic adventure, and thought he'd waste your time here rather than keep shopping - much less costly. (Oh, I finally found a Spotmatic Eye Cup!)

If I understand correctly, the coating of lenses was first done to reduce light refraction as much as possible - thereby brightening the image considerably - especially on multi element lenses. With more use of colour, further correction was added to cure a multitude of UV and Haze issues. Multi Coating followed and the necessity of Sky and UV filters was virtually eliminated except to physically protect the lens.

Now, the filter presents us with two more refracting surfaces. Do filter manufacturers take the care Pentax does to coat their
filters for refraction as well as for their intended purpose? I've noticed that there are various qualities (and prices) of say, Hoya. Along with the various thicknesses, there also appears to be a variance in f stop compensation. Would this have to do with the more expensive versions being refraction coated?

Are cheap filters defeating our expensive lenses?

Is there a simple, refraction-treated filter that can be used for lens protection?

If anyone can (or cares to) answer this, can you also tell me where I left my keys?

Thanks for your considerable patience!


Link Posted 12/10/2005 - 13:33
Yes, I've found filters to affect the image quality.

For example, had a cheap 49mm UV filter on the SMC-F 70-210mm, changed it for a Hoya Pro-1 (99.7% light transmission they say), and the contrast was muchly improved... didn't try comparing against the lense minus the filter sadly.

Apparently, Kenko do Pro-1 filters in the Far East and seem to have the same specs as the Hoya Pro-1 but at vastly reduced price (I'm given to understand that Kenko, Hoya and Tokina are the same group).

That's about all I know for now!


Link Posted 12/10/2005 - 13:52
I think you'll find your keys in your jacket pocket, the one you wore this morning when you nipped out for a paper!
Die my dear doctor, that's the last thing I shall do!


Link Posted 12/10/2005 - 14:10
You're BOTH right!
Now I can drive to the camera shop for Pro -1's (after I stop at the bank).


Kim C

Link Posted 12/10/2005 - 14:30
As well as the Hoya ones, I have found the B&W MRC ones to be very good.



Link Posted 12/10/2005 - 17:04
My preference is for the Pentax SMC filters or the delightfully heavy B&W in their brass mounts.

Coating and multicoating is to prevent reflected light from bouncing around inside the lens and causing flare and loss of contrast. An uncoated four element lens might lose 35% of its light transmission in this way. This is reduced to well under 5% with multicoating, even in the most complex zoom lenses.

Multicoating is one of the major factors making lenses with large numbers of elements possible.
Best regards, John


Link Posted 12/10/2005 - 20:14
B&W was already a favorite of mine and now you tell me they make good CAMERA filters too? I know they filter their scotch to perfection - so why not?

OK, Hoya and Kenko Pro, B&W and of course the rare Pentax are top of my list.

George Lazarette

Link Posted 12/10/2005 - 22:13
Personally, I think filters are a good way to ruin a good lens.



Link Posted 12/10/2005 - 22:24
They can be, George. I only use filters where necessary these days, and with digital cameras that's not much!

Mainly down to Tri-X and a red filter for film....
Best regards, John


Link Posted 12/10/2005 - 22:35

George is about to save me a WHOLE bunch of money.

Goerge, if I've got SMC Pentax lenses, and am using them under the proper conditions, I should take the protective UV filter OFF and simply be careful? I have nice hard sunshades for my 135 and 200 Super Taks which should protect my lenses from all but the worst sand storms - and I live in Canada.

As for my short lenses I'll .... ooooooooooppps...

Back to eBay...mutter.


George Lazarette

Link Posted 13/10/2005 - 00:05
Every filter in the world, no matter how well made or expensive, will degrade your image to some degree.

Cautious people slap cheap filters on their lenses to protect them. I prefer to take a little care and get the full benefit of my expensive glass.

You can apparently stub a cigarette out on a Pentax lens without damaging the coating. I haven't tried it myself.

With film, as JR says, there are some occasions when filters are necessary, but with digital there are very few. The only time I would contemplate a filter with digital would be shooting landscapes in hazy conditions, but a better bet, if practicable, would be to come back at a less hazy time. Lens coatings are not designed to remove ultra-violet.



Link Posted 13/10/2005 - 03:58
Mac wrote:
You're BOTH right!

Glad I could be of assistance, perhaps you could return the favour and tell me where the heck the remote control for my VCR has got to........again

Like most people, I normally find it lurking down the side of the sofa but this time, the house-goblin has really surpassed himself!

On the subject of filters, the general purpose UV, Skylight and Polarisers have no real detrimental effect. A reputable manufacturer uses high quality glass which is machined and polished to a very high standard. They are perfectly flat and therefore do not increase the barrel / pincushion distortions that lenses already have. They have no magnifying effect and the screw fit versions are fixed so close to the front element that they are totally invisible to the lens. The only effect is the colour cast or polarising effect that they are designed to produce. They filter out the unwanted rays that would otherwise be detrimental and I can't see how the combined affect of the filter and multi-coating can harm the image.
Harmful colour casts can be compensated for anyway, particularly for digital images.

Special effects filters are good fun and can result in dynamic and exciting images but they should be used sparingly because the effects can become obvious and tiresome but we're not talking about these here!

I've never damaged and had to replace a filter and therefore would not have damaged the lens itself but I'd much rather wipe a greasy fingerprint (we've all accidentally touched a lens' surface or spat on one when trying to blow off some dust - be honest......well I have ) or a raindrop from a relatively inexpensive filter - no matter how tough the coating on the lens is supposed to be.

If there is an optical difference between a lens with or without a UV or skylight filter (in terms of image resolution), then I doubt very much whether the vast majority of users would be able to tell
Die my dear doctor, that's the last thing I shall do!


Link Posted 13/10/2005 - 11:19
Kimbo, appreciate your input as always! Thanks!
I have quite a collection of used filters of unknown origin. Is it safe to say that Hoya, Cannon, Tiffen etc. filters in metal rings inscribed with Made in Japan are better than similar items in plastic mounts silk screened with Made in the Phillipines?
I'm really looking crosseyed at my PL filters now - both Circular and Linear. That's FOUR refracting surfaces that need coating and therefore $. I didn't pay much for them brand new.
One of the reasons I've been concentrating on early Pentax equipment is the 49mm standardization of the wide-through-shorter tele lenses - I don't need a collection of filters for each and every lens.
Time to cull through the LowPro wallet severely.

Now to the important stuff. The fastest way to find a mislayed article is to replace it.

Ask me how many remote controls I own - or keys - or ...

The worst part is that the toughest items to find are those that I purposely put in a new, inventive and clever "safe place".

My short term memory probably ain't what it useta was, but I'm not sure - I can't seem to remember....

Maybe I should take a picture of my brilliant storage spots. That way I'll only have to develope the film to find my stuff. Now where did I put that camera.....


Link Posted 13/10/2005 - 15:33
Nots' to worry Mac, I've found it

The sneaky little devil hid it between the sofa cushions, it had been missing for two days and trust me, apart from looking everywhere else, I'd all but taken that sofa apart. I'd removed the cushions, tipped the sofa upside-down and even checked inside the lining underneath and it absolutely wasn't there. I was the last person to use it and no one else had seen it since - whoever said that inanimate objects don't move by themselves?................'coz they bl**dy well do!
If I ever catch that goblin, he'll be well and truly evicted, I can tell you

Anyhow back to matters photographic, I suppose now that digital photography is so much more convenient than film (oh dear), I could try some 'with and without filter' shots to see if there is a noticeable quality difference. If there's nothing obvious at 6.1MP then I shouldn't think it'd visible on standard sized prints. Slide film tends to be more critical and the images are often projected at very large ratios but the quality of the projector lens also has to be taken into consideration - can't wait until digital projectors become affordable
Die my dear doctor, that's the last thing I shall do!


Link Posted 13/10/2005 - 15:51
Kimbo - try this link:

Digital image to slides for 1.35
I've heard the quality is superb.

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