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Reflector vs Refractor

Mehraj Anik

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Allow me to further complicate this discussion by asking another question. Has anyone had any experience with the much advertised JMI binocular reflectors?

Jonathan

Hello Johnathan

Yes, I have a pair of JMI RB-10's at school. I got a really nice grant from the Amgen Corporation and spent the whole thing on these beauties. With 250mm aperture for each eye, and up to 160x magnification - they are absolutely amazing to behold. It is hard to describe the contrast and detail that using both eyes brings out.

They are very comfortable to use, in spite of their size. The 50kg bins sit on a perfectly balanced Alt-Az mount, and the eyepieces are at a perfect height for an observer sitting on a comfortable piano stool or similar. Since you look down into the eyepiece and the tubes are pointed up over your shoulder, you essentially see what is directly behind your head. This turns out to be a very natural position to observe in, and you very quickly get used to it. The bins are steered about using a comfortable set of padded handlebars that have controls for focusing each eye independently, and for setting inter-ocular distance, and for binocular collimation (x and y axis for each eye independently). All these functions are motorized and run off an internal, rechargeable 12V battery. When using good eyepieces at lower powers (below 50x), the eye relief and focus are so forgiving that they don't need to be adjusted much between viewers - which is good, because focusing and inter-ocular distance are interdependent, and achieving perfect focus is significantly more complex than with a regular telescope or bins. You have to tweak these two adjustments together, and then do it for each eye independently, and then do it with motorized controls, not with traditional twist-knobs. Rather like pointing an EQ mount, once you develop the technique, its easy enough, but it isn't something you let just anyone fool with. I understand from Jim Burr (the inventor and manufacturer) that the new RBX series solves this problem for the most part.

The views are stunning. Color, resolution, contrast - and yes, that 3-D feel to things. I know intellectually that my eyes cannot be seeing depth, but the brain fills it the details and the perception is very real. The Moon in particular is amazing - rather like flying over in a jet and looking out the cockpit window.

If you get a chance to view through one - do it! If you have the money to purchase one - you won't ever regret it... and you will have a scope that will be the star of the show where ever you go. You can see the size of them in the photo below.... and no, in case you are wondering, the grin never comes off your face. Others find it a bit unnerving after awhile, but once you let them sit down at your giant bins, grab the handlebars and zoom about the sky for a bit, they have the same grin on their face, too.:)

You can see my Flick photostream of uncrating and assembling them for the first time HERE.

Dan

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chiltonstar

chiltonstar

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Interesting that the refractor vs. reflector debate is still live and well....good to know that some things never change.

Isn't there an old adage that "the best telescope is the one you use most often" - might be a different answer to the title of the thread depending on whether you live in a dark site with few neighbours, or in West London with streetlighting like daylight!

Chris

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MikeWilson

MikeWilson

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I was about to chip in until I saw Dan's humongous ostentatious minigun of a binoviewer and almost fell off my chair when I realised it wasn't April the 1st. Certainly budget blowing but I can already see the benefits (a quick contrast test using one eye and then both eyes through a good pair of binoculars demos the effect). Now to convince my wife that I need these...

As for what type of scope? Well, it's largely an academic debating issue but it boils down to a couple of things in the end. Do you want to use it for planetary visual, deep sky visual, planetary imaging or deep sky imaging? Do you need it to be portable or not and .... is there a scope that ticks most of your boxes available in the For Sale section? :)

I moved from my Mak-Cass (long focal length, slow) to a Newt (smallish focal length, fast) which essentially doubled the speed and halved the focal length. I also have to collimate it and it's harder to store.

I'm thinking about moving to a short focal length refractor for imaging on the basis that I now have intermittent access to a dark site and a smaller scope would be easier to travel with. It could also make a better grab and go option. I'm also thinking about upping the size of my reflector from 6" to 8" and going from f/5 to f/4. Not much bigger, but bags more light for the time so more efficient use can be made of the dark sky when I get to it.

Decisions, decisions.

Mike

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spaceboy

spaceboy

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Based on a sensible beginners budget for a new scope there are two budget scopes to consider in the Refractor vs reflector debate.

Evostar 120 Achromatic refractor on EQ5 = £425. Good contrast on the moon but suffers from false colour and fringing on planets and bright stars. Gives good wide FOV's on some of the larger open clusters M44, M45 and so on. Can also offer views of DSO but not with any real distinguishing detail. M13 can be resolved reasonably well under ideal conditions but no where near as well as a larger instrument. More portable than the larger 200p and requires less maintenance. Cool down is significantly shorter due to the closed tube design. Optics have to be well looked after as you are looking through them as apposed to at them. Some find refractors difficult to look through when looking at zenith which is often the best place to look at objects as there is less atmosphere to look through.

Explorer 200p Reflector on EQ5 = £420. No false colour. A lot more aperture for your money. Offers much more detail when observing DSO's but lacks the contrast on the moon. Planets IMO look better as there is no CA or fringing. Can be a pain to use on a EQ mount as the focuser position can end up in some odd places but some find it acceptable to turn the OTA in the tube rings until comfortable for viewing. Faster F/ratio usually means you need good quality EP's to get the best from the views. Cool down times are longer and the open tube can suffer turbulence. OTA is large and can be a handful when mounting or storing. Requires collimation more frequently but the mirrors can gather a fair bit of dust before cleaning is deemed necessary.

Given the choice I agree with Uranium235 choose both then you can't go far wrong :):D.

No seriously! IMHO a regular guy with a regular salary, wife & kids and other commitments should go with the reflector. This will keep you happy for a long time before you consider needing an upgrade. If your not a regular guy and have money to burn? I would still say go with the reflector as even with an apochromatic refractor there is only so much looking at planets you can do before you get the calling to go hunting them really hard to find DSO's and only big aperture are going to reveal them.

But as the others have mentioned there are other designs to consider first. MAK, SCT, Klevtsov, MAK-NEWT.

SPACEBOY

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"Humongous & ostentatious"??? Not so friend. Col Gadaffi with his gold-plated AK-47 is ostentatious, Barak Obama's deficit is humongous, but my little RB-10's are just 'efficient'... the smallest package for that much scope that you can possibly imagine!

Consider that compared to the cost of buying a pair, just flying over here to spend a few days playing with them cost's pennies by comparison. And once your spouse has a go with them, no convincing will be necessary - she will be convinced that you are a genius or an idiot, and after that - nothing you say will ever change her mind again! :eek::o:)

Heck, I'll even spring for the Guinness and the sandwiches! We can set up the C-11, the Apomax refractor (133mm f/12) and the RB-10's... you can play in the land of the giants!!!! :)

So.... when's your flight get in??? :eek:

Dan

I was about to chip in until I saw Dan's humongous ostentatious minigun of a binoviewer and almost fell off my chair when I realised it wasn't April the 1st. Certainly budget blowing but I can already see the benefits (a quick contrast test using one eye and then both eyes through a good pair of binoculars demos the effect). Now to convince my wife that I need these...

Mike

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todd8137

todd8137

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hi and welcome ,i have both a reflector and a frac the frac is 90mm and 900mm long its both good at pics with dslr camera and web cam and gives the best crispy images of the planets and esp the moon ,the reflector is also good at short expo pics with the 12"dob i usally do 30x 4secs and stack them works for me deep space and planets are both easy with the reflector and the web cam takes good planet stuff they both good in there own ways

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  • 3 years later...
RikM

RikM

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What size mirror diameter would equal the picture taken with a 4 inch refractor /30 second exposure?  BrockW

It depends what you mean by 'equal'. Do you mean equivalent brightness, equivalent field of view, equivalent resolution? You need to provide a bit more detail about what you are trying to achieve. There are many potential answers.

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ronin

ronin

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The f number is the important factor, not actually the aperture.

An f/7 10" reflector will need a longer exposure then an f/6 3" refractor.

And the other way round, a 10" f/8 refractor will need a longer exposure then an f/6 3" reflector.

Forget aperture, except to work out the f number.

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