Support Astromart! | Log In | Help
Astronomy NewsTelescope ClassifiedsTelescope AuctionsTelescope Articles & ArticlesTelescope Articles & ReviewsTelescope and Astronomy ForumsAstronomy Events Calendar
Review Categories
Search Reviews
Submit Review

User Name:

Password:

Save Login
 
New to Astromart?
Register an account...

Terms of Service
Privacy Policy
Help & FAQ
Astronomy Links
User Profiles
Top Users List
Sponsors
Supporters
RSS Feeds

Home > Reviews > Telescopes > Refractors > Questar 3.5 vs. TV-85

Questar 3.5 vs. TV-85
By Malcolm Bird - 7/14/2013

| 5 Comments... |

Gee, what do you do when you find yourself with 2 iconic scopes in their own field and an alt az mount that can swing them both at the same time?

I know! Let’s compare them.

I recently found myself the owner of a Questar 3.5 standard and a TV-85 at the same time as I was trying out a heavy duty Alt-Az mount from Canadian telescopes.

This article is not intended as an in-depth review of either scope (you can find in-depth reviews on both scopes elsewhere on this site), but more a contrast of technologies and approaches.

Let’s take a look at what we’ve got.

Questar 3.5.

This is probably one of the oldest iconic scopes in the business. It was developed in the late 50’s and has remained largely unchanged to this day. It is a 90mm F14.4 Maksutov Cassegrain mounted on a dual tine fork mount with single axis RA drive. It is industrial art – think Swiss army knife meets ETX meets Liberace. The Q3.5 is eye candy. From its deep purple silk screened star map to the polished aluminum mount, you just want to touch it. It looks great just sitting on a bookshelf. Everything on the scope is made from finely machined and polished aluminum.

It is renowned not only for its high optical standards but for its unique rear control box that allows a variety of views and functions to be selected by flicking levers.

TV-85

The TV-85 is an 85mmF6.3 APO refractor and is regarded by many to be the pinnacle of short focal length APO refractors. It and the TV Pronto before it (and with whom it shares the same body and tailpiece) pretty well defined the small APO refractor ‘look’ for the world and approaches the design aesthetic from a more scientific point of view, preferring a buttoned down black on white motif. (Evergreen is also available)

The TV-85 also uses finely machined aluminum for its parts, but has preferred to go the black anodized route and to use a lot more of it. You wouldn’t think twice about zipping it into its padded case and tossing on the back seat of the car. You wouldn’t be so cavalier with the Q3.5. Not that you couldn’t, but it’s sort of like a boiled egg vs. a Faberge egg kind of thing..

Test Mount

The Alt Az Mount used was a Canadian Telescope HD Duo mount rated for 60lbs, so swinging these two smaller scopes at the same time wasn’t much of a challenge. One of the neat features of this mount is that the head for the secondary scope (opposite the main scope on other side of pier) has its own two axis mount so you can bring the second scope coincident with the main scope. Very handy for doing side by side comparisons…

What you get.

When you buy a Questar standard or Duplex, you are essentially getting a complete telescope system. Everything required for Astro or terrestrial use is contained in a single fitted 7 x 7 x 14 leather or vinyl luggage case. Questar sells the Q3.5 main scope and mount with RA drive, 2 Brandon eyepieces, an internal selectable 2X Barlow, an internal selectable finder, a solar filter (and an integral one for the finder too), power cord and legs to convert the scope from Alt Az to equatorial mode. Truly an observatory in a box! Oh yeah – and the case it comes in.

Older used Questars in nice shape with the standard accessories listed above typically sell for $1800-$2500. For this test, the complete scope and mount were affixed to the Duo mount.

The TV-85 is sold only as an OTA with a nice 99% Everbrite diagonal and their excellent 20mm Plossl eyepiece. Period.
If you want a finder, a mount, another eyepiece, a Barlow or anything else to make it a usable observing system, then that is extra. TV-85 OTA’s can be found used for $1000-$1500 depending on included accessories, but in order to bring it up to the same accessorization level as the Questar, you would have to purchase an equatorial mount, a second eyepiece, a barlow, a finder and a solar filter.

Caveats for Q3.5

The observatory in a box approach of the Q3.5 comes unstuck when it comes time to use the scope in equatorial mode – ie: serious Astro use. The table top legs are OK for quick peeks (in which case, just use it in Alt Az mode), but they are not practical for any kind of serious observing. You need to find a tripod to get the eyepiece up to a comfortable observing height (and away from elbows on the same table that scope is sitting on..) As the Q3.5 is only about 7lbs, you won’t need a heavy duty tripod, and it’s just the tripod you need, as the Q3.5 already has its own mount. I use an aluminum EQ1 tripod with a homemade wedge which is more than up to the task. These can be found for a song.

Another caveat of the Q3.5 is that it operates at F14.4, so it has a very narrow field of view, and a fairly long focal length, so if you are craving sweeping, low power/wide field views, this is not the scope for you. You are also limited to 1-1/4” format eyepieces, so the lowest power you can achieve is with a 32mm plossl – yielding 45X and about 1.3* FOV. Although it does have a built in finder, it is a very wide field/low magnification affair and has no crosshairs, which combined with the narrow F14.4 optics can make it a chore trying to find things at night.

Caveats for TV-85

The TV-85 has the opposite problem. The same 32mm Plossl that provides a marginal FOV in the Questar essentially renders the TV-85 into a giant finder scope with 18X. With only 600mm of focal length, to get anywhere near the advertised maximum of 225X you will have to resort to exotic short focal length EPs, or creative use of Barlows and EPs. Eg: 3X barlow with an 8mm EP.. or buy a finder for it.

Another factor is the weight. With a diagonal, finder and EP on board, the TV-85 is approaching 10lbs. That is 40% more than the complete Q3.5 setup – mount and all, and well beyond the capabilities of any standard photographic tripod. It is almost overbuilt. Its lens cap is machined steel….it would stop a bullet. So you’ll have to buy a good sturdy mount whose capabilities will only be limited by the thickness of your wallet.

With the Q – you take it out of the box and start observing. When you receive your TV-85, you still have some more shopping to do to make it a useable system..

Fit and finish

The Q3.5 is the Swiss army knife of telescopes. It packs a lot of utility into its diminutive package. Everything is machined aluminum and has been deliberately designed and crafted to be light weight. Everything operates with a smooth, if light, feeling of precision. The silk screening on the sliding dew shield is the envy of the industry, and has attempted to be copied by several mfrs over the years. The Q3.5 is an instrument, not a tool – if you follow me on the distinction.

The TV-85 is finished just as well, but adopts anodized aluminum finishes rather than polished. As mentioned above, it has a heft to it when you first pick it up that is surprising. It’s heavy for its size. It has a nice split clamshell that allows the OTA to be rotated and slid fore and aft for a balanced and comfortable viewing position. This clamshell has several tapped holes for mounting to a tripod or to a mount rail.

Later model TV-85’s come standard with their nice 10:1 Focusmate focus reducer. (it was available as an option on earlier models.) It provides a nice smooth dual speed focusing action. In fact, I couldn’t imagine using the scope without it as the focus point on any fast optical system comes and goes over a very short distance, and a coarse focuser makes it that much harder to hit.

Optics

If you do the math and factor out the central obstruction on the Q3.5, these scopes have virtually the same primary light gathering surface area. So I was absolutely stunned to discover what a huge difference in brightness existed between the two scopes. Whether I was looking at star fields, the moon or daytime use, and with both scopes operating at the same magnification, the TV-85 was hands down visibly brighter than the Q3.5. I have run across websites that have described the Q3.5 as a ‘dark’ scope. Now I know what they meant.

Part of this is attributable to the designs – being a refractor the TV-85 only has a total of 3 optical surfaces where light losses can occur. (in/out the objective and a bounce off the diagonal mirror). The Q3.5 has 6 before it reaches the eyepiece. (in/out corrector, off main/secondary mirror and in/out of the diagonal prism) Even allowing for equal antireflection/transmission coatings, the Q3.5 would lose twice as much light as the TV-85, which in today’s world of 99%+ claimed efficiencies would probably only mean 3-4% to the TV-85’s 1-2%.... And this is before factoring in the eyepieces….

However, most of the Q’s that any of us will ever look through, including mine, are over 30 years old. And while they may have had state-of-the-art coatings back then, they’re inefficient by today’s standards. This is starkly obvious when you compare the two scopes. Even switching the TV Plossl’s out of the TV-85 and replacing them with the Questar Brandons visibly dimmed the view. I have always been a skeptic when it came to believing the advertising claims from the scope mfrs regarding their coating efficiencies – and I suppose that from one generation to the next, these differences would indeed have been incremental, but to see the accumulated differences that 30 years makes in one jump is startling….

Both scopes have razor sharp optics with no ambiguity in the focus point. Both can be pressed to high levels of magnification (for their aperture) without the image breaking breakdown. Both scopes provide very satisfying images. And both scopes remove that niggling question as to whether it is the seeing, or is it the optics….?

Beyond the issue of light throughput and associated contrast, it was a tossup as to resolution. It will be the seeing that will be the limiting factor as to what these scopes can show.

Real world use.

As mentioned before, the finder on the Q3.5 is not great for night use. Its small aperture and extra wide FOV combined with lack of crosshairs and the main scope’s excruciatingly narrow F14.4 FOV makes finding things a chore. It is better used on bright objects like the planets and the moon. Messier marathons are out of the question (although I am sure there are some diehard Q owners out there who would dispute that) Daytime use is easier as light gathering is not a factor, you can guesstimate the center FOV and if you’re out a bit, you can still see lots in the main field to guide you to your intended target. At night, a miss is a lot harder to rectify – sorta like dropping something in a dark room and not knowing which way it bounced..

The TV hardly needs a finder because at lower powers it functions as its own giant finder. The downside here is you have to start out low and work your way up by switching out EPs.

So which scope is for you?

At the risk of offending rabid Questar users, I would have to say that the TV-85 is more of an Astronomy purist’s scope. It excels at wide field viewing for terrestrial or wide field Astro sweeping, and can be pressed to useful higher magnifications for serious Astro use. To own a TV-85, one has to do so strictly for the optical pedigree and build quality. Don’t misunderstand - it is an excellent telescope, but in the end, the TV-85 is a refractor - a very good one, granted, but the focuser goes in and out, and you change eyepieces and Barlows – just like every other refractor in the world.

Paradoxically, the very portability and utility that was intentionally designed into the Q3.5 also necessitated certain compromises - (F14.4, small finder, everything to fit in the one case) These compromises detract from its usefulness as a serious astronomical telescope – even though I am quick to point out that it is still an excellent 90mm instrument if you can accept the caveats mentioned above. My first telescope was a 50mmF12 Tasco refractor (back when that meant something..) and I would have died and gone to heaven if I someone had given me a Q3.5 back then….

But when it came time to sell one of them, I kept the Q. Why?

Using a Questar presents the user with an experience you cannot get with any other telescope. The ability to carry the complete scope and tripod out in one hand, the ability to choose either Alt-Az or equatorial use, the ability to choose finder, low power and high power views with a flick of a lever, the completeness and thoughtful design and the fact that you are using a piece of history.

And that means something to me.




del.icio.us   Digg it   Reddit   Twitter   MySpace   Stumbleupon  

Funding Member
Funding Member
Telescopes, Astronomy,
Binoculars


Advanced Search...

All times are in (GMT-8:00) Pacific Standard Time Zone  
Astronomy News | Telecope Classifieds | Telescope Auctions | Telescope Reviews | Telescopes | Telescope and Astronomy Forums | My Account | Help | RSS