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Checking my thinking, please


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Hello

I've been researching refractors and can get the TMB-92 for £1,700.An f/5.5 apo with FPL-53 ED glass. Collimatable lens cell, 13.25" long, nice and portable/light(ish) at about 4kg, with a 3"dual speed Feathertouch focuser. Retractable dew shield, dust covers, and aluminium hard case. Review here ...

http://media.skyandtelescope.com/documents/TMB-92.pdf

I'd still need to buy a finder, diagonal, lenses and tube rings, and I think a flattener for imaging, but wondering what people think of this scope. It doesn't seem to be in widespread use. What else should/could I consider for that sort of price that has a decent R&P focuser? Intention is to use it for visual, but also to get into DSLR imaging.

Thanks for the thoughts.

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Alistair that is an awful lot of dosh for a smallish refractor, are you sure you want to spend that much on what I presume is your first scope? If you are a beginner and are set on a refractor then there are many much more cost effective options out there. For instance you can get a Skywatcher Equinox 120 APO for about 500 pounds less, it will outperform the TMB and it will still be a scope you can grow into for years to come. Take my advice and do a bit more research before you buy, posting here was a step in the right direction, I am sure you will get many helpful replies and reap the benefit of others hard won experience.

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Ok, I just looked. How easy will it be to start out imaging with a scope of 900mm focal length? Also, will the Crayford be up to me hanging a DSLR off the back end? Ian King basically warned ne away from Crayfords and said R&P is the way to go.

Any other suggestions?

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You use a focal reducer to bring the scope down to about F/6 and a crayford is perfectly adequate for use with a DSLR. When you start hanging filterwheels, off axis guiders etc as well as a camera things are then not so clear cut. If your main interest is imaging as opposed to visual work then your best bet will be an 80mm ED, again with a focal reducer/field flattener. This is probably the easiest introduction to astro imaging but it is true to say that "easy" is a relative term here, the learning curve is steep and a lot of the kit out there is not plug and play! I don't want to discourage you but you need to be aware that it will be a while before you are producing images you are willing to share with others. So my advice for a beginning imager is use a smallish refractor, again the Skywatcher 80 Equinox Pro seems good value, mount this on a capable german equatorial (the HEQ5 as a minimum) and guide it with a finderguider and decent guide camera (QHY5 is ok). There are any number of other perfectly good combinations but that lot is a fair start and will set you back less than just the TMB optical tube alone.

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Paul, I have found time and again it is cheaper in the long term to buy the best you can afford right up front. The old adage "you get what you pay for" is particularly true here.

Alistair, Bern at Modern Astronomy will sort you a finderguider, he is one of the good guys along with FLO and Ian King, I am sure there are others but those are the people I use for 90% of my purchases.

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Paul, TMB has a reputation in the States for being excellent equipment, designed by the late Tom Back, if you want to research, go to the Cloudy Nights forum. For visual and AP without going overboard in expenditure, the best bang for your buck is probably the Altair-Astro 115 ED triplet at £1250, for this you get a 3" crayford focuser CNC tube rings and an excellent illuminated 60mm finder. Olly P. has done a report on this scope which can be seen on Altair-Astro`s web site, I think I did mention to you that Brantuck has this scope and couldn`t be more delighted with it I understand :)

John.

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Thanks. I'd read about the TMB on CN, was just looking for any UK experiences and also wondering about alternatives.

There is a waiting list for the AA115, but it will be cleared with the next delivery expected in May. The other alternative is the AA 102, the 115's little brother, and that is in stock. Both seem great options and I've seen the 115 review. I guess I'm just cynical that they might have picked the very best scope for the review. Didn't Deneb have to return a couple? Nothing wrong with that of course, it happens, and it gives AA a chance to shine with customer service which I think they did, but it just leaves a lingering doubt at the back of my mind until they are producing them in volume.

Notwithstanding any issues though, still very interesting scopes and great pricing.

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Alistair that is an awful lot of dosh for a smallish refractor, are you sure you want to spend that much on what I presume is your first scope? If you are a beginner and are set on a refractor then there are many much more cost effective options out there. For instance you can get a Skywatcher Equinox 120 APO for about 500 pounds less, it will outperform the TMB and it will still be a scope you can grow into for years to come.

The 900mm fl/F7.5 might be a bit long for begining imaging? Even with Skywatcher 0.85 focal reducer (another £180) it only becomes a 765mm F6.3 which is still quite long & slow for deep sky in my experience.

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With a good mount, you'll have the basics of a nice imaging setup with the TMB. A lot of imagers swear by their Feathertouch and the addition of that focuser is certainly one reason that scope isn't cheap.

The only thing you need to keep in mind is that a 90 mm refractor will produce disappointing visual views compared to a 6" or 8" reflector. If visual is a reasonably high priority for you then you should consider this. It's less of concern if your skies are dark: you'll then get some nice wide-field visual views which a lager scope can't dish out. Nevertheless, a modest reflector will be resolving a lot of stars in the larger globulars whereas a small refractor will show you a fuzzy patch. A friend of mine recently bought a nice 120 mm refractor to go alongside his 8" Dob. His final analysis was that he gets better DSO and planetary views with his much cheaper Newtonian. Just something to think about...

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