A True Light Travel Scope--Possible?
Posted 05 November 2013 - 09:01 PM
There are expensive options, but I am not looking for pristine optics...just average with decent field and light weight. I tried to C90 and their are some small cassegrains or Maks that might work but using these in the field with a wide variety of users is a real problem when the focal ratio is f/10-13. I have a problem with that restricted FOV as well.
So, I have on hand and readily use a Stellarvue SV80 FM2 finder scope. It is not designed as a travel scope. But why not? So I wrote them. This is how I put it....
I need a 3 pound scope (it is 2.5 pounds). I need FOV for my use and the use of lots of newbies in far away places or even close to home. Why not change the optics (it actually makes the optics easier to produce) so instead of a 3.75 focal ratio we have a 5 or 5.5. Take the fixed dw shield and make a way for it to come off easy. Put a short piece of Vixen bar on the bottom instead of just treating the mating piece as a finder scope. Voila! Travel Scope! Less than 3 pounds, a rotating back, decent field...
I have not heard back. This kind of solution (for any vendor willing to fill the niche) gives you a modest performing refractor, very light weight, and it could fit on anything from a desk mount to a light tripod to stick. With 2 EPs and a diagonal you have a whole kit.
I wonder why someone does not do it? SV has the tube already. It is light and strong. Someone makes it. And, in the end, you also have a beginner scope that is very competitive but lighter than the standard 80 short tube designs.
So, I am interested to see if they hear me. I mentioned that my other thread got 600 looks in 48 hours. I think the market is there, but who am I? Just a user with a need.
In the meantime, I am taking my SV80 FM2 and making it my travel scope. It is cheaper than the short tube designs and vastly lighter. It is 1/4 the cost of the expensive options.
What do you think?
Posted 05 November 2013 - 11:22 PM
What do you think?
This is what I think:
The Orion ST-80 was mentioned several times in the previous thread. It seems like it fits your needs perfectly. The OTA is under 3 lbs, it's 80mm F/5, the dew shield slides off easily. They are rugged. It comes with a pad to mount the scope on a tripod. The barebones OTA is $120.. what is there not to like?
Posted 06 November 2013 - 12:05 AM
What do you think?
This is what I think:
The Orion ST-80 was mentioned several times
It's already been available for many years, fits the criteria you've spell out, and priced right so that you won't have a fit when you loose or break one. Buy used, they are even cheaper. Celestron had one years ago (spotter version), orion has 2 versions of a 80mm short-tube, ioptron has them in several colors with tracking mount, and I'm sure there are many other generics out there.
Posted 06 November 2013 - 02:40 AM
71mm fluorite - $1200 with a couple of extras
77 ED - $895 for OTA
89ED - $1395 for OTA
Borg stuff comes up for sale on Astromart at times and sells for a reasonable discount. I think the 77ED would be good for your needs.
The Borg fork mount is very light but is not the smoothest thing in the world. There will be a mount called the Free Turn 1 from Half Hitch mounts that will be 3.5# and only $395. Later, the company is thinking of making an even lighter mount.
Posted 06 November 2013 - 05:05 AM
The refractor OTA weighing 3.25 lb. is made from the lens in cell from my William Optics 72 FD. I make a new tube with a simple helical focuser in place of the stock tube and 2-speed focuser.
A small Vixen guide mount with slow motion control on both axes (1.25 lb).
A Sirui T-1005X photo tripod (2.5 lb).
A 6x30 fincer, diagonal and 2 eyepiece (3 lb).
K W TONG
C8+CG5 GT, TSA102+HEQ5 PRO, MK67+Voyager, NexStar 6SE, C5+Mizar K, WO ZS80FD+Kenko NES, Megrez 72FD+Kenko KDS, Mini Borg 50, PST
Posted 06 November 2013 - 07:48 AM
Posted 06 November 2013 - 08:06 AM
It is very stable when supporting my little refractor but it has limited travel in both axes. I have to build a simple “elevating platform” for it out of two pieces of aluminum angle.
Posted 06 November 2013 - 09:15 AM
If you care about wide field viewing with modern wide field eyepices, you may find that at f/3.75, it is impossible to keep the entire field in sharp focus, and that the outside will be so far out of focus that even excellent eyepieces will show astigmatism.
This is why the vast majority of finders are only really suitable as finders. You dont' really need your finding stars in perfect focus and in the vast majority of them, they won't be.
But that is not the supplied eyepieces doing it, it is the horrendus field curvature of the scope itself.
There used to be a samll Petzval you could get. Maybe William Optics or something. Much flatter field.
So, consider the field curvature carefully.
My own advice is that unless you are willing to take the risk on re-sale if it does not work out, you may want to find something with a bit slower focal ratio.
Or maybe not. Lots of people have told me over the years that they only care about performance at the center of the field, and if you are in that camp, then this small fast refractor may be perfect for you.
Posted 06 November 2013 - 10:05 AM
I just happen to already have the FM2, and some of its features are unique that would be helpful. The scope with its diagonal and an EP are less than 3#. If I could get the vendor to buy into a couple changes, it would would further increase its suitability.
We use C8s a lot for outreach and training. So our FM2 ends up doing double/triple work. It is already set up for light/quick adaptation to scopes if not used separately. In our case, this helps.
Other options, as discussed on the other thread, are available, but the prices go up very fast. If you were with me going to some of these places, price and weight drive the train. It has to walk where I go, be put up in a hurry, and if its use incurs damage or I pass it to others, it has to be replaced without major financial cost. The Antares was a little to heavy but the price was right; the ST-80 falls in the same class.
It may sound minimalist, but some places we go, hardware is really scarce. And, when it is around, it might get used for something else. When you have a light system (meaning around 3#, you can actually mount a scope with one standard ring and attached the ring to a handle...the handle is bolted with enough friction to a board...you have just made a two axis manual mount. I have done this because the cost and size of a tripod (even a light one) plus the scope to faraway places gets out of control real fast. And, as previously said, the tripod is attractive hardware for lots of other things.
These are the sorts of things we work through when we go places. However, for schools and villages, if they actually make the little homemade mount, they "own" the solution and want to protect and keep it. So there is method to this kind of approach.
Posted 06 November 2013 - 10:31 AM
Posted 06 November 2013 - 11:43 AM
You are right, Jon. It is the closest thing to the Antares I used and almost the same weight. With diagonal and EP added plus a couple rings...it's 3.8 pounds plus a couple added. That puts it out of reach, however, for most light tripods. Outside of that, these are great.
I am not quite sure where you are getting your numbers.. I happen to have four ST-80s, I just weighed three of them with diagonals, all three were within an ounce or two of 3.0 pounds.
For a photo tripod, the included mounting blocks are effective. As far as rings, you only need one ring, not two.. My favorite ST-80 has a two inch focuser, I work it at 200x on doubles, one ring is plenty stable...
An ST-80 has a real focuser and a very reasonable focal ratio that is workable at higher magnifications. I use them as loaners on lightweight photo tripods and they work and certainly are at F/5 are far more capable than an 80mm F/3.75 finder, I have one of those.. as Eddgie says, field curvature is nasty and at moderate to higher magnifications the CA is devastating.. but I guess you probably know that.
(Photo of Ioptron ST-80 fitted with Orion focuser on Fairfax $10 garage sale, 3.0 pound tripod, it all works and weighs 6 lbs total)
Posted 06 November 2013 - 03:49 PM
Posted 06 November 2013 - 07:53 PM
Posted 06 November 2013 - 08:09 PM
Posted 06 November 2013 - 09:39 PM
To me even more problematic than the FC is the almost non-existent diffraction limited depth of focus with such scopes. We're talking microns that can be counted on our fingers and toes. Good luck with that, using a cheap focuser such as is often shipped on such OTAs.
The depth of focus at F/3.75 is about 30 microns. To get a good focus, that does require a top notch focuser. But really, with an 80mm F/3.75, focusing would be done for individual colors, not the entire spectrum.
One thing about an F/3.75 scope, if you are using a 1.25 inch focuser, optical length of the drawtube plus the diagonal can only be about 4.5 inches, otherwise the drawtube cuts into the light path. Since a 1.25 inch diagonal has an insertion length of about 3 inches, that means a 1.25 inch Drawtube..
My University Optics 80mm finder is F/3.75 and setup to focus with an RA diagonal. It had a short focuser but it was long enough that the effective aperture was only 60mm.
Posted 07 November 2013 - 12:54 AM
My 80mm Stellarvue NH weighs about 8+ lbs just for the OTA, so I have wanted to get a much lighter setup for hiking or other high mobility activities.
Posted 07 November 2013 - 06:33 AM
I use a Borg 77 Achro as a travel scope. Instead of a tripod, I travel with a Car Window travel mount and improvise. The attached photo is the Borg 77 equipped for Solar H alpha. The improvisation was a locally purchased G Clamp.
Posted 07 November 2013 - 11:36 AM
$63 for a little more aperture in the same basic set-up.
It might be interesting to try one of these and see if it would work for your purposes. If so, you could almost afford to drop-ship a half dozen or so to the nearest larger city/town and have spares in-country to take into the bush. You could actually afford to leave them when you depart, which might be appreciated by your outreach guests.
Posted 07 November 2013 - 02:41 PM
...even more problematic than the FC is the almost non-existent diffraction limited depth of focus...
Jim makes a valid point here. One of the things I like about the 60mm SV finder is the "slow" thread of the helical focuser which helps a lot in this regard.
Posted 07 November 2013 - 03:57 PM
The Celestron travel scope that Jim mentioned looks good, and I am not familiar with it. I know the tripod is junk and pieces a plastic, but if the optics are average and I can point the thing, that means a villager "outback" can do it. Don't know how tough it is and amazon reviews are generally from non-regular observers, so I cannot read to much into the ratins. Does look like a possibility.
Several have suggested things below 80. While I would like to look at the little 70 travel scope, one reason I don't go much below 80 is because we get better bang for the buck by simply using an affordable binocular. You have to think in terms of schools and way out there. It's not a straightforward decision in developing regions: do you want a 60-70 refractor or a 8x42 binocular? Our kits generally have both a small refractor and a binocular. If I could take only one and I am really cramped, we usually opt to take 8x42 binoculars (bushnell H2O) or even 7x35 (bushnell Falcons), 68 and 25 dollars respectively. Serious observers in the developed areas usually laugh at this, but they generally don't go where we go...and usually don't understand the local limitations. Believe it or not, this solution works when a scope can't be shipped in, and still covers a lot of ground.
Thanks again, all. BTW, Stellarvue did get back to me but no real revelation. Their lighter weight 80 is nice and would fit the weight class of the short tube designs; their optics are very good. The price is much higher, however. For me in this nice developed calm region with money, it's fine like many others. In the backwoods in the Philippines and Uganda...nope.
Posted 07 November 2013 - 04:31 PM
Posted 07 November 2013 - 11:07 PM
Posted 08 November 2013 - 02:58 PM
I'm using the scope shown for my super portable option: a 60mm SV finder on a monopod. It's true that an ƒ3.75 finder will have significant field curvature but some eyepieces are helpful. Naglers and ES82s seem to have a complimentary FC that is very corrective. The 14 and 18mm ES82s are especially nice. Orthos also do well since I suspect they sweep much of the problem under the field stop. The setup in the photo gives me 9x and a TFoV of 4.66º. It is also very flexible with EP choices and filters. The setup weighs about 4.2# including the monopod. Due to hand held issues, the monopod limits me to about 18x (a 12.5 ortho) but I'm OK with that.
PMJI, but I love this idea, with the monopod. Might even be able to use the monopod with and ST80 or AT72ED.
Attaching a long cord/ string to the monopod, with something on the end that you can step on as you are using a monopod, can help a great deal with steadying a monopod and is a very cheap solution. I've used that with a camera on the monopod and it should work ok with a wide field scope. Of course, a light tripod works well.