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Camera lens question

Thalestris24

By Thalestris24
in Discussions - Cameras

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Thalestris24

Thalestris24

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Hi all

I was just looking at a second hand 500mm lens. The seller is upfront about a small scratch on the coated front element and which can be seen on a photo of the lens. They say it doesn't affect normal use but I'm wondering if it would likely cause a problem with astro use.

Any thoughts/experiences?

Thanks

Louise

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ChrisLX200

ChrisLX200

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If it's just the coating that has been removed then no, it probably won't have any significant effect. However if the scratch is in the glass then it may act to produce a diffraction spike - in which case the size of the scratch is everything :)

ChrisH

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Thalestris24

Thalestris24

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7 minutes ago, ChrisLX200 said:

If it's just the coating that has been removed then no, it probably won't have any significant effect. However if the scratch is in the glass then it may act to produce a diffraction spike - in which case the size of the scratch is everything :)

ChrisH

Hi Chris

It looks superficial but difficult to tell with certainty and I don't have any experience of scratches... Here's a pic:

Scratch.PNG

It doesn't look much and the lens otherwise seems in good condition - it's for sale via a dealer

Thanks for your input

Louise

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Thalestris24

Thalestris24

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10 minutes ago, happy-kat said:

That's faster and longer reach then an ST80.

If the price is right...

It's just under 3x the price of an ST80 but, although not apo, should be better than achro and with a flat field on an aps-c sensor. On the other hand, it is a lens, not a scope and the scratch is of concern...

Louise

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Thalestris24

Thalestris24

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Easy to say! I'll sleep on it... I've written to ask the seller whether there are any diffraction spikes when pointed at bright lights against a dark background... However, I figure most photographic dealers don't know much about AP!

I've no doubt that someone here, at some time, must have come across a slightly scratched refractor front element? Anyone?

Louise

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ChrisLX200

ChrisLX200

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17 minutes ago, Thalestris24 said:

Easy to say! I'll sleep on it... I've written to ask the seller whether there are any diffraction spikes when pointed at bright lights against a dark background... However, I figure most photographic dealers don't know much about AP!

I've no doubt that someone here, at some time, must have come across a slightly scratched refractor front element? Anyone?

Louise

Well I was using this before I thought something didn't quite look right with the images - not awful mind, just not as sharp as I usually get...

DSC00826_zpsipmnwexx.jpg

So I don't think you'll notice the effect of one 1/4" scratch much. Seems a reasonable price @ £279, but make sure the lens is all tight and nothing loose. Dealer is offering a 30-day refund anyway?

ChrisH

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Thalestris24

Thalestris24

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He he - but I don't see any scratches on yours! I see you looked it up - now what are the chances that a pristine one appears for sale tomorrow, and cheaper!!??

I also don't know whether there might be any infinity focus problems using it with a Canon though there's always the option of attaching a ccd.

Louise

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Xplode

Xplode

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I wouldn't worry about a small scratch like that.

All Asahi lenses focus nicely with a Canon DSLR.

I can''t see from your image if it's a regular Takumar og SMC Takumar...if it's not SMC i would not have bought it myself

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Thalestris24

Thalestris24

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2 minutes ago, Xplode said:

I wouldn't worry about a small scratch like that.

All Asahi lenses focus nicely with a Canon DSLR.

I can''t see from your image if it's a regular Takumar og SMC Takumar...if it's not SMC i would not have bought it myself

Hi

Yeah it's a Super Multi-Coated one :) I'm not sure about infinity focus with a canon. I had to adjust a 200mm f4 to get infinity focus and I couldn't get infinity focus with a 400mm f5.6.

Louise

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Thalestris24

Thalestris24

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3 minutes ago, Xplode said:

Normally there should not be problems with focus, was in a modified camera?

I think I tried the 400mm with an unmodded 550d and a low profile adaptor. I ended up, er, taking the lens apart. Sadly, I've not been able to reassemble it, d'oh.

Louise

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Thalestris24

Thalestris24

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2 minutes ago, Xplode said:

I've had several M42 lenses and never had a problem with focus with my 6D.

Could have been a problem with your lens since technically it should be able to reach focus if everything is as it should.

It's possible there is/was a problem with it. They are funny lenses with all the optics in the front section and empty space in the rear. I'll have another go at fitting the two sections together again. It's been problematic trying to get the male and female threads to mate though they were obviously together originally, lol

Louise

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Thalestris24

Thalestris24

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Just a quick update - looks like someone bought it yesterday afternoon. Anyone from here?? I'd decided against it anyway. Apart from the concerns I raised before, I read that although it had good contrast, the resolving power wasn't great. I might have snapped it up if the price was ~£100 less but for only £90 more I could get a SW 80ED with superior optics. In any case, I already have a TS triplet apo which is excellent, so a lens at the same fl would be superfluous really. Still, I hope whoever bought the Takumar enjoys it!

Louise

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ollypenrice

ollypenrice

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A bit late, but there is a video or article 'out there' about someone gradually trashing a lens in a step by step manner and taking a shot at each stage. Not until it looks as if it has been hit by a land mine does much happen to the image.

If a scratch gave diffraction artefacts the trick would simply be to blacken it. Just remind yourself of what the secondary mirror of a Ritchey Chrétien looks like in the light path...

Olly

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Thalestris24

Thalestris24

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1 minute ago, ollypenrice said:

A bit late, but there is a video or article 'out there' about someone gradually trashing a lens in a step by step manner and taking a shot at each stage. Not until it looks as if it has been hit by a land mine does much happen to the image.

If a scratch gave diffraction artefacts the trick would simply be to blacken it. Just remind yourself of what the secondary mirror of a Ritchey Chrétien looks like in the light path...

Olly

Thanks Olly, but, yeah, much too late! Lens was sold yesterday and I'd decided it probably wasn't such a good buy and would have been superfluous anyway. Still, for the future I'll bear in mind the feedback I've received here :) 

Louise

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