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Thread: .5.focal reducer with field flattener

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    Default .5.focal reducer with field flattener



    Hi all, I am considering getting a focal reducer, about .5
    I have es ed80, asi1600mm. I already have an estimate field flattener.
    My scope is f6.
    Can I simply buy a .5 reducer since I already have a flattener?
    Do I have to get a combo? If so, any suggestions?
    Thank you!


    Adam
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    Default Re: .5.focal reducer with field flattener

    I have a couple .5 reducers and they make poor paper weights. And they will not cover the 1600 chip size.

    Just my experience,
    Steve
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    Default Re: .5.focal reducer with field flattener

    50% is a significant reduction and unless it is a matched design for your focal length and aperture it will introduce a lot of distortion and noticeably degrade the overall image quality. As noted by sdbodin the smaller low cost types will not evenly cover an imaging chip. F6 is already a pretty fast scope so angular distortion is going to be pretty bad if you reduce it into the f4.4 range. They are "ok" (as in far from ideal) for visual use, but definitely not for imaging. If you look at the Tele Vue or Vixen reducers, you will see that they are larger diameters and offer less drastic ratios to preserve image quality.
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    Default Re: .5.focal reducer with field flattener

    Why exactly do you want a .5 reducer? The ES80 already has a pretty wide field.
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    Default Re: .5.focal reducer with field flattener

    Quote Originally Posted by Trombatissimo View Post
    F6 is already a pretty fast scope so angular distortion is going to be pretty bad if you reduce it into the f4.4 range.
    Note that f/6 will be reduced to f/3 with a 0.50X reducer. You are already having troubles with your filters causing halos at f/6, wait until you see the halos that you will be dealing with at f/3. I definitely do not recommend a 0.50X reducer with your current setup!
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    Default Re: .5.focal reducer with field flattener

    I have an f/6 scope and run a 0.8x FR/FF with little problems... (Although, I do get halos)...
    I wouldn't push my rig any further unless it was a true APO or even better, a quad. The pinpoint correction just isn't there..
    My 2¢... YMMV
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    Default Re: .5.focal reducer with field flattener

    You guys are awesome. I had no idea it would cause so many issues, which is why I asked!
    I would to do widefield, I have some crappy lenses and didn't want to spend another fortune on a nice lens. I probably will... That's why I was asking about a reducer. For now I'll use my 50mm old Canon lens I have, from the 70's. I bought a small adapter, it fits. I had to stop the lens a lot, and am doing an image now. I may consider a larger lens 85, 105, or 135 prime lens. Any suggestions that wont break the bank? I am ok purchasing used if I have to.

    Thank you guys a bunch!! I thought oh I have a decent scope,.I can just reduce it vs buying a new lens lol. Oh well, good thing I asked

    Adam
    Lowjiber likes this.
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    Default Re: .5.focal reducer with field flattener

    Those guys were doing this when Lassie was a pup and Moby Dick was a minnow. I've learned more just reading their threads than anywhere else. (This is a great place to learn.)
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    Default Re: .5.focal reducer with field flattener

    Quote Originally Posted by Ruthlessaz View Post
    You guys are awesome. I had no idea it would cause so many issues, which is why I asked!
    I would to do widefield, I have some crappy lenses and didn't want to spend another fortune on a nice lens. I probably will... That's why I was asking about a reducer. For now I'll use my 50mm old Canon lens I have, from the 70's. I bought a small adapter, it fits. I had to stop the lens a lot, and am doing an image now. I may consider a larger lens 85, 105, or 135 prime lens. Any suggestions that wont break the bank? I am ok purchasing used if I have to.

    Thank you guys a bunch!! I thought oh I have a decent scope,.I can just reduce it vs buying a new lens lol. Oh well, good thing I asked

    Adam
    Sorry that I forgot to return earlier to this thread. You can definitely get excellent results with older used SLR lenses. Most of the improvements in newer lenses concern themselves with decreasing the close focus distance and improving the resolution and distortion at these closer distances as well as the upgrades to the electronics - none of which matter for Astrophotography. You can adapt other brands (ironically the Canon FD breech mount is the only legacy mount that doesn't permit infinity focus with a simple adapter ring) with the two most popular lenses being the Nikon 180ED (180mm Extra Definition) f/2.8 and the current Korean built 85mm f1.4 lens sold as a Rokinon, Samyang, Bell & Howell, and several other "brands". Most older 85mm lenses are pretty good at infinity focus, but good fast aperture brand name ones will probably cost more used than a new Korean lens. It also benefits from modern coatings, an aspherical element that helps a lot with CA at large apertures, no accumulation of years of dust, and it comes with the EOS mount. The Canon FD 85mm f1.2 is excellent, but pricey and it requires a mount conversion to work directly on an EOS body.

    The suggested Nikon is the king of the older "200mm class", but for a lot less money you can use an f/4 200mm lens from Nikon, Pentax, Olympus, or Minolta that will be just as sharp at the slower aperture as the Nikon is at f2.8. The speed is an advantage, so the Nikon remains the top recommendation. There are many 135mm manual focus lenses that are also excellent performers. Most of the older f/2 135mm lenses need to be stopped down to give sharp stars at the edges, so this will be your cheapest option by buying any good brand name f2.8 135mm lens. If you get lucky, you may find an affordable Leica Elmarit-R 135mm 2.8, but any Nikon, Pentax, Olympus, or Minolta 1970's or 80's version lens (older ones have less effective coatings) will give excellent images.
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    Default Re: .5.focal reducer with field flattener

    Another +1 for the Nikon 180/2.8 ED lens. Optics are apparently identical between the AF and MF versions of the lens (Although the AF will only work on a Nikon body with focus drive motor). For Nikon owners, it also makes a nice general use telephoto.
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