Does this exist? Should it?

Seems like there are a lot of achromats out there in the f8 to f10 range. Would it improve things to stretch a mass produced achromatic objective to f12. How about a 90 mm f12 achromat with a 2-inch focuser on a simple alt-az mount as a first scope, supplementary scope kind of offering.

What should it cost? Could this be a price/performance sweet spot?

I'm looking for something to interest a really bright 8-year-old nephew who has expressed an interest in the sky. I think collimation would be a bit much, so a Dobsonian is out. This imaginary scope is what I would like to find.

Steve

Meade used to make a 90mm f/11 alt/az achromat with a two inch focuser as you describe. It is called a DS-90, and can also be upgraded to GOTO if desired.

Meade no longer makes this scope, but I occasionally see new "old stock" available at various online auctions and such.

Steve, I've wondered about this myself. Perhaps I'm mistaken but isn't it easier to produce a longer focal length lens of a specific quality, than a shorter f.l. of the same quality. Maybe I've got it backwards & that explains the flood of short f.l. instruments on the market in the last few years. I don't recall back in the late 60s-70s this being the case.

As cheap as equatorials are being made, it seems like someone could come up with a high quality alt-az for $200.00 or so, on a sturdy tripod. DR

Yes, it does exist, and has been around for quite a while.

I've got a Vixen 80mm f/11.3:
http://www.mindspring.com/~jeffpo/vixen.jpg
There was also a 90mm version. And I think Orion made some and maybe Celestron. Meade? Haven't seen one with a 2" focuser. Most seem to be .965" and 1.25".

Mine is on an easy to use alt-azimuth mount with slow motion controls. It's my grab-n-go scope. Gives great views of the moon and planets. I've followed moon shadow transits across Jupiter and have easily picked up the Red Spot. It does a decent job on the brighter deep sky objects. If I were giving a recommendation, I'd say go with a 90mm like you suggest.

Jeff

Bill Vorce has the Meade 390/395 models in parts. I bought a 90mm (f/11, multicoated) achromat in aluminum cell, the original Meade baffled tube for the 90mm lens, and a dew shield from another scope. Received it in parts and assembled it. The dew shield needed some tape on the cell to fit snug. He had the 1.25" plastic and metal focuser, but I wanted a Synta/Vixen style with dovetail finder mount. I found this on Astromart. All completed I have $75 in the scope. It is not to bad.

Of course, there still is the purple fringe at high power. I think I might purchase a minus-violet filter. I can also use it for my ST80.

Bill also sells the alt-az mounts and finders that were supplied with the Meade 390.

Surplus Shed sells a $10 mirror diagonal.

This would be a great project for you and your nephew to work on. It will give him a better understanding of optics and a better appreciation for the sky.

Check this links on the Meade 390/395 :
http://www.geocities.com/CapeCanaveral/Lab/8501/

http://www.photostop.net/395.html

http://www.meade.com/manuals/m395/

Hope this helps. Keep us updated, please.

Clear skies,

Tim Hornbeck

The Terra Hoc and Star Hoc 90mm refractors (1000mm f/11.1) utilize 2-inch focusers and are available through Hardin Optical (Canada).

The 90mm achromat has always suffered a sort of "middle child" reputation, due to two important factors:
-size/bulk
-price/cost
In a nutshell, there isn't much difference between most 90mm achromats and 100-102mm achromats -- whether we're talking aperture, overall size/bulk, or price.

The "good side" of this minimal difference:
A good 90mm achromat can perform at a level quite near that of a good 4-inch achromat.

The "bad side" of this:
A good 4-inch achromat can be purchased for about the same price as a good 90mm achromat -- oftentimes, *exactly* the same price.

So, the customer's question becomes, "Why not just get the 4-incher? It's really not much bigger, and they cost about the same."

Indeed, most potential buyers do just that: opt for the 4-incher. Others go for the $$ and bulk savings and choose an 80mm achromat (which, itself, performs very similarly to a 90mm achromat).

The second-hand market does include some interesting 90mm achromats from the past, including rare birds such as a Vixen 90mm f/15. It's always a kick when those goodies show up on Astromart.

Best wishes.
-Dan

I purchased a Celestron Firstscope 90 f 11 on Astromart for under $60 and replaced the objective with a Vixen Research Grade achromat. Same size, f.l., slipped right onto the existing tube. Had to tune up the focuser a bit, but it is a delightful little telescope now.

I did the same thing with a 4" f 15 achromat tube, and it's my favorite now, on a G-4 mount I picked up for $200.

Another alternative you should consider would be the Orion 90mm Maksutov. It is not a refractor, but meets your same criteria:

- It doesn't require collimation
- It is f/12

It does not, however, have a 2" focuser. You could easily mout this on one of Orion's alt/az mounts.

I have not used one of these, personally, but they tend to get quite favorable reviews.

-Jake