Skylight Filters and Focus (1 Viewer)

griffin · Nov 3, 2003

Further to a thread sometime ago I have a query. I am using a Apo 77 and have recently added a Jessops 77mm Skylight Filter 1A ( JessS177) to protect the objective lens. This Filter screws on to the scope no problem but it appears to affect the focus, particularly on 60x zoom. The difference when taking off the filter is obvious and others have agreed. It is obviously less noticeable on 20x, but still there. I am told it should make no noticeable difference - but it does !

Has anyone experienced similar problems and can any of the boffins offer a reason as to why a simple filter can cause this anomaly. Incidentally, has anyone tried the Leica filter ? It costs £80, which I personally think is a rip-off, however if it works I would consider getting one - a tiny bit of the coating was removed with realtive ease on my 62 scope and I am anxious to prevent this happening with my new 77, though the hood protector is more useful on the this scope.

Cheers

Lindsay

griffin · Nov 10, 2003

Okay,

I should maybe have posted this in scopes forum not the digiscoping forum.

It does effect the sharpness of photo's too though !
Have subsequently bought the Leica filter.

LC

grahams · Nov 11, 2003

Lindsay Cargill said:
Further to a thread sometime ago I have a query. I am using a Apo 77 and have recently added a Jessops 77mm Skylight Filter 1A ( JessS177) to protect the objective lens. This Filter screws on to the scope no problem but it appears to affect the focus, particularly on 60x zoom. The difference when taking off the filter is obvious and others have agreed. It is obviously less noticeable on 20x, but still there. I am told it should make no noticeable difference - but it does !

Has anyone experienced similar problems and can any of the boffins offer a reason as to why a simple filter can cause this anomaly. Incidentally, has anyone tried the Leica filter ? It costs £80, which I personally think is a rip-off, however if it works I would consider getting one - a tiny bit of the coating was removed with realtive ease on my 62 scope and I am anxious to prevent this happening with my new 77, though the hood protector is more useful on the this scope.

Cheers

Lindsay

I have a UV filter on my Swarovski scope and using a Nikon 4500 do not get any focusing problems except possibly at 60X magnification on the scope and full zoom on the camera when I find it is difficult to focus the camera manually. The filter I used is a Hoya.

scampo · Nov 11, 2003

You seem to be having some bad luck.

I suppose you might have got some flare into the scope from the sun or a bright reflection - but this would be a one off rather than a consistent problem. Otherwise, I really cannot imagine how a plain filter of this kind can affect the quality of sharpness in any way - very odd. I would take the whole lot to the shop where you bought the filter and ask their advice.

Regarding coating coming off your telescope lens - again, very odd. The coatings applied to all lenses are extraordinarily hard. Also I think that a slight mark on a lens coating will not affect the physical properties of the lens at all.

Andrew Rowlands · Nov 11, 2003

Hi Lindsay,

Unless you use the highest quality filter you can find (try Nikon, Canon, Olympus, Zeiss etc.) you will probably notice degradation of definition.

Try holding the filter in front of the lens/objective, whilst looking at an object, then removing it. With cheaper filters it will make an obvious difference!

Any extra glass layer, will add something; internal flare to odd colours etc., unless it is specifically designed for the task.

Flare, as Scampo has mentioned will also be an issue, any filter will have the effect of 'shortening' any lens hood.

This can be 'recovered' by the addition on an add-on ?rubber? hood, screwed in turn to the filter. This could offer better protection in poor weather, if the threads make a good seal. Check for tightness regularly!

You may find that the use of a rubber hood will afford you enough protection, without losing any definition (it may sometimes improve it by cutting down on flare), it will give more area for the wind to shake the scope, though, so make sure you have a decent tripod.

Cheers,

Andy.

scampo · Nov 11, 2003

Whatever the name on the rim, it's my experience that many filters are made by one company - Hoya. I have never seen a filter that seriously degrades an image, and certainly not sharpness. Even the Cokin type plastic / gelatin type filters don't do that.

Andrew Rowlands · Nov 11, 2003

scampo said:
Whatever the name on the rim, it's my experience that many filters are made by one company - Hoya. I have never seen a filter that seriously degrades an image, and certainly not sharpness. Even the Cokin type plastic / gelatin type filters don't do that.

I think that the answer lies elsewhere other than with the filter myself.

My experience in testing says that they DO degrade. How 'serious' it is is subjective.

Andy.

scampo · Nov 11, 2003

I bow to your emboldened experience then, Andrew.

(-:

After thirty-five years of involvement in photography with close connections and awareness of the photographic trade my experience is as I explained. Apart from flare or dirt, I would not expect a half-decent lens filter to be causing such an obvious degradation of the image quality.

Andrew Rowlands · Nov 11, 2003

scampo said:
I bow to your emboldened experience then, Andrew.

(-:

After thirty-five years of involvement in photography with close connections and awareness of the photographic trade my experience is as I explained. Apart from flare or dirt, I would not expect a half-decent lens filter to be causing such an obvious degradation of the image quality.

Half-decent? -

scampo said:
Whatever the name on the rim, it's my experience that many filters are made by one company

- make your mind up!

I tested, with my previous (60mm) scope; 62mm filters from 3 manufacturers; with a 15x eyepiece; a Japanese camera manufacturer, Hoya (that you mentioned), and a 'lesser' brand. It was a dull winters day with a high contrast subject at over 100 yards with 15x eyepiece. I found the more expensive the filter, the less the effect.

Andy.

Al Downie · Nov 11, 2003

I tested, with my previous (60mm) scope; 62mm filters from 3 manufacturers; with a 15x eyepiece; a Japanese camera manufacturer, Hoya (that you mentioned), and a 'lesser' brand. It was a dull winters day with a high contrast subject at over 100 yards with 15x eyepiece. I found the more expensive the filter, the less the effect.

I'm also very surprised that you were able to discern a difference between filters, particularly if you were taking your eye away from the scope for long enough in between tests to fit the filters properly.

Al

Andrew Rowlands · Nov 11, 2003

How do you choose which 'scopes to buy?
Do you test them against each other?
And bins?

Andy.

scampo · Nov 11, 2003

satrow said:
How do you choose which 'scopes to buy?
Do you test them against each other?
And bins?

Andy.

You clearly seem to know your stuff, Andy - but I do wish you would read emails carefully before firing off a rather haughty response.

As far as I can see, the physics of the thing suely dictates that the chances of a - yes half-decent - skylight filter reducing the sharpness of an image noticeably is very slight indeed. As I said, I have used many single gelatin and plastic filters and never noticed any important image degradation apart from that caused by flare.

griffin · Nov 11, 2003

Guys, Guys Guys !

This thread has gone from being a non starter to a flame war !

Thanks for your points - you all have important considerations.

However, I agree with Andy. There IS a difference, at least in my experience with the 77. The Leica Filter I bought is PERFECT, but very expensive at £80. The Jessops ( £28 ) one was creating image distortion at all magnifications - thats a fact, other people viewed it and agreed. Why its doing it I have no idea, but it is. If you have got a jessops one working fine then I say good for you for saving £50 !

I haven't tried a Hoya, but suspect they are similar to the Jessops one ( also Japanese ). I didnt want to spend another £40 on a Donkey. I contacted Leica and they asssured me that it would not degrade the image quality and it doesn't.

Re the coatings I have not been unlucky or careless. I have it on good authority from a Leica Dealer no less that Leica scope objectives are notorious for their coatings coming away, even after simple cleaning as recommended in the manual. They have sent back quite a few. Steve, you may be right but mine is going back to Leica - I have not paid £700 for something to mark that easily with light and careful use. Hence the paranoia about getting a filter that actually works. Al, get a Filter for your 62 - with that short lens hood its asking for it.

Was going to buy Leica BINs - no chance of that now. Will check out Avians or something that I dont have to worry about scraping over bushes etc.

Linz

Andrew Rowlands · Nov 11, 2003

Ok, Scampo, I'll try another tack - Quality Control.

The 'top' manufacturers can afford it, whether the item is manufactured in-house or not. They pass this cost on to the customer, in the form of higher prices; better warranties come into play here too.

High street suppliers, even if the same manufacturing plant is used, usually have items of a lesser quality. This can, and does, vary enormously. Of a box of say, a hundred such items, perhaps 70% are of reasonable quality, 20% poor and 10% very high quality, close to or as good as those 'creamed off' by the big names.

Apologies if my earlier posts appear haughty.

Try visiting an optician if you can't see the 'edit' button.

Cheers,

Andy.

mak · Nov 11, 2003

satrow said:
Ok, Scampo, I'll try another tack - Quality Control.
The 'top' manufacturers can afford it, whether the item is manufactured in-house or not. They pass this cost on to the customer, in the form of higher prices; better warranties come into play here too.
Cheers,
Andy.

Not true. Costs are not passed on simply because of quality control.
Now about the filter. By adding another glass your transmission is reduced, as light is lost when light passes through each glass to air surface. The light transmission loss can also differ, depending on the type of coatings used, and whether it is a mutilayer coating or single layer etc.
However I cannot understand why you should have a focussing problem when the filter is fitted, especially if it is a quality filter.
Why not contact Leica, as generally the manufacturers are only too willing to assist with your enquiries.

Andrew Rowlands · Nov 11, 2003

mak said:
Not true. (SNIP).

The thread is quite long but it is worth trying to read it.

Andy.

griffin · Nov 11, 2003

Someone on the last Skyight thread sometime ago tried a Hoya Pro Filter on his Zeiss and said that it noticeably degraded the image quality. So my experience is far from unique. Interesting that its a different make of scope and filter too.

However, I felt this was somewhat inconclusive hence I started this thread, with worries about protecting my new Leica 77. I have now found a solution in the Leica UV 77 Filter and this functions with no detriment to the optical quality, and I am happy, though 80 quid lighter.

On mine it ( the Jessops ) not only changed the colour cast ( to be expected ) it actually made the image blurred - not possible to focus sharply at any mag though obviously worse at 60x ! This is undisputable and not a figment of my imagination, or due to a faulty scope etc.

I would suggest anyone interested in UV/ Skylight filters to try some at a shop and put them through their paces, but this is not always possible in which case beware : two wrong filters could end up costing more than the Manufacturers recommended version. This was my dilemma - though I only made one bad purchase.

Linz

mak · Nov 11, 2003

Happy to hear that you have sorted out the problem. Hopefully £80 well spent.

Andrew Rowlands · Nov 11, 2003

Hear, hear, well said Linz.

Andy.

Al Downie · Nov 11, 2003

Al, get a Filter for your 62 - with that short lens hood its asking for it.

I did. I bought a Sigma EX (multi-coated on both sides) for £18; it makes no perceptible impact on the optical performance of the scope.

Al

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