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happy-kat

filter attachment to large lens

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Thinking about whether to sell some bits and swap in a used canon 200mm f2.8 legs though that has a 72mm thread so using a 2 inch filter on that is going to lose some of that aperture seeing as the lenses is ok astro wise wide open and the camera I have is mirrored I don't have any back focus distance to play with.

Advantages are the lens is good for wildlife as well.

Disadvantages how do I get around using a 2" filter without losing aperture or buying another camera even if second hand.

Alternatively look at a field flattener for the 50ED I already have.

Advantage I already own it and could use a 2 inch filter with just 2mm loss of aperture.

Disadvantages not so great for wildlife photography as the helical is slower to react and adjust focus with. It's slower at f4.9. (Starizona I gather could be bringing out a FF for mirrored DSLR used on ED50)

I've tried searching but haven't found an answer to the filter issue. Any thoughts happily received.

Edited by happy-kat
Changed title

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It's the filter attachment question I haven't been able to answer. Any ideas gratefully received.

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I've assumed there's not enough back focus room on a canon 200mm f2.8 lens to fit a filter between the lens and camera at the back end, I'm guessing there would be if a mirrorless or astro camera was used.

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Sounds like you can use clip in filters.

You have a Canon 1100D ? That has an APS-C crop sensor, the 200 f2.8 is I believe an EF mount ?

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Yes thank you I could, but I do not want to use a clip in filter as the lens is commonly used for general daytime, though a clip in filter would solve the immediate question but doesn't have great long legs unless I sold it.

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Sounds like you're after some sort of short extension tube that can take drop in filters.

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First question, what filter are you talking about? Astro or conventional photography?

For astro, it strikes me you have two choices: find a solution to a large filter on the front, or a clip-in filter. I've no experience of clip-in filters, but can't you simply remove it when you want to do conventional photography? This is the cheapest solution I would have thought, if you can get the filter you need as a clip-in filter. Then again, can you get astro filters in the size you need (72mm)? Plenty of conventional filters of that size though. I can only think that if you want an astro filter on the front, you'll need to somehow use an existing filter ring and insert the astro filter into that. Perhaps a step up ring might give more options re. sizing. The only way you'd be able to use a drop-in filter between the camera and lens with an extension tube is to use a mirrorless camera which has a much shorter lens flange-sensor distance. You can't add an extension between the camera and lens with your DSLR otherwise you'll turn the 200mm lens into a macro lens! Fine if that's what you want to do, but not for astro :).

My 2d worth anyway.

By the way, what do you mean by 'legs'?

Ian

 

Edited by The Admiral

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1 hour ago, MarkAR said:

Sounds like you can use clip in filters.

You have a Canon 1100D ? That has an APS-C crop sensor, the 200 f2.8 is I believe an EF mount ?

From what I have read the EF mount lenses can be used on the (APS) EF-S bodies, but not the other way around. So it shouldn't be a problem I guess. It just means that the full frame image will be cropped so that the field of view with the APS camera will be the same as a 320mm lens on a full-frame camera.

Ian

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I already use EF lenses on the APS-C 1100d body it's great as pretty much no vignetting.

I already own a 2" astro filter and use various step rings to connect to the different lenses, though none of those chop more than 4mm off the lens apertures. The 200mm is a 72mm threaded lens so stepping that down to 48mm is quite an aperture hit when the lens is good to use wide open.

I am considering a narrow band duo filter and is part of my evaluating whether to get a FF for the ED50 or sell that and get a Canon 200mm l f2.8 (SH).

Anyway you confirmed my thoughts it is either an astro cam or mirrorless to be able stick a filter on the back of that lens between the lens and camera.

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39 minutes ago, happy-kat said:

Anyway you confirmed my thoughts it is either an astro cam or mirrorless to be able stick a filter on the back of that lens between the lens and camera.

Sorry, I don't understand why a clip-in filter would not be a consideration, that is, assuming you can get dual/triple band as clip filters? Surely, even if you have a 2" filter already, it's going to be cheaper to purchase a clip-in filter than either of the options you suggest. That's not to say an astro camera wouldn't be a useful development for your set-up. If you can stand the financial hit then to my mind it would be the right way to go, rather than another DSLR/Mirrorless. Also, do we know what sort of performance the new Canon mirrorless cameras have for astro (I take it that your camera hasn't been astro modded), and can BYEOS work with it? An astro cam would at least bring a good Ha response to the game. Then again, I do understand the advantages of having a self-contained unit. Not an easy question to answer!

Ian

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I have been pondering for a while now and my limiting factors are:

1 Get the most out of what I already have

2 be mindful of my foot print and raw resources, so second hand appeals

3 less is more, there is usually more that can be gained from 1 then often not yet squeezed

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14 minutes ago, MarkAR said:

Canon Ra would be a good option.

It would, presumably as it's designed for astro. Are there any astro reviews of it around yet? Mind you, it comes at a price and I can't imagine there are many 2nd hand examples around as it's just been launched.

Ian

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Hi happy-kat, You can get clip in dual band filters if you Google 'em. I already use a clip in Ha filter and UHC filter in my DSLR's and don't find a problem removing them when required. I use them with my Samyang 135 mm lens which would otherwise take 72mm filters on the objective. You could then keep your existing gear. 

I've also looked at dual filters but note that as Ha will usually dominate the level of OIII from an object and you can only expose for a given time (unlike if you had seperate filters and could expose OIII for longer) the benefit of a dual filter may be quite subtle. Also I understand that OIII is more prone to the effects of moonlight unlike Ha as much.

If you live in a light polluted area you might want to take account of the pass widths of the Ha and OIII bands, if they are too wide your imaging time will be affected by the local sky fog. 

Cheers,

Steve

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Thanks Steve.

That's my concern with the UHC, it has a wider pass band on the second peak then a duo filter and I had wondered if that might be a loss of filtering in an LP area..

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55 minutes ago, happy-kat said:

the UHC, it has a wider pass band on the second peak then a duo filter and I had wondered if that might be a loss of filtering in an LP area.

Yes it's the worst concern with the UHC filter, until the internal Canon IR filter cuts out red light at 700 nm you have quite a wide opening for any local light pollution to enter the optics-

 

Transmissionsgraphik

I once tried to best guess the amount of coverage of the two pass bands around OIII and for Ha/SII with the Canon IR filter in place, this was around 85nm in total for the two pass bands that's quite a hole.

This is the spectrum for leds so still 20-30% of light would get through-

image.png.68cb52817831003ce58ed77eb32bdbd4.png

And the spectrum of some other types of lighting-

image.png.994dd4600f3c9d04ad06f1b3ebe42b99.png

There is this filter with a much slimmer pass bands-https://shop.stcoptics.com/product/astro_duonarrowband/ but quite costly.

I hope this helps happy-kat in coming to a decision on the way forward.

Cheers,
Steve

  • Thanks 1

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That illustrates my thoughts and the spectrum graphs are very useful as well, thank you. Even 20-30% pass on lighting is way better than getting the lot right now so is 

The L-enhance by optilong has a narrower second peak and is second on my list but the UHC has high % of wavelength pass in the ranges and good product QA.

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