Posts Made By: Tom Mengel

That’s about right – think the diameter of the shaft of light coming into your scope (say a 80mm in diameter shaft for a ST-80) divided by the power (say using a 26mm EP to give you 16X). The “exit pupil” (the diameter of the shaft of light coming out of your EP) would then be 80/16 or 5mm. Some people have up to 9mm dark-adapted irises, and as we get older (or if there is too much light to become completely dark-adapted in the first place – like most “suburban” areas) our maximum iris diameters will be less. I’ve heard the new standard is about 5mm for light polluted areas and for older observers, but mileage will vary.

BTW – the 7mm “standard” was set during WW-II (and before) by many Navies in the world that came up with the almost universal 7mm maximum as the figure for an “average” young sailor’s maximum dark-adapted iris diameter who had to stand watch, hence why the 7X50s became a almost world-wide watch bimolecular standard. This was an extremely important issue before the invention of RADAR as visual spotting of the “other guys” first could be the difference between your swimming (and maybe becoming shark bait) or sailing to your next port. As a 50mm objective was considered the minimum aperture to see a ship at 26 miles (60 foot superstructure seen over the curve of the earth from another 60 foot superstructure) and 7X gave the right “average” pupil size for maximum light throughput at night. 7X50s were also light enough for the sailor to hold reasonably steady for the 2 to 4 hour session involved. My Dad worked on this among other things at the predecessor of the Navel Research Lab outside of Washington DC at the time and told me how they came up with these things - smile.

Hope this helps to explain it ...

FWIW - TM

Canadian stereotypes aside, Thanks Tom!

I'll go get some for my 8 inch SCT. Only problem is which logo to get ...

Also remember that your eyes can get "lazy" in the dark trying looking at a point source. I tried some binoculars that were supposedly spot on. Worked great (even in the dark) until I was tired. I happen like to spend an hour or so before bed out on the deck with my 12X60s so I began to notice that if I was really tired at the end of a long day the star images would split and I'd have to concentrate to get them to merge again. I also suspect some manufactures may merge the images at less than infinity if they think the binoculars will be used mainly close-up during the day.

Folks who use Binoculars and Bino viewers on telescopes at star parties also notice big differences in how different people can "merge" the right and left images.

I suspect this may be an issue with some folks who run into "the star splits" even on well-aligned optics because their own eyes merge images a bit differently than "normal" folks. My own solution is to have binoculars I can align myself to fit their use with my own eyes. But of course your mileage may vary.

FWIW - TM

No - but it would seem to be pretty simple.

How about a screen with some guide marks (typing paper?) and a post or clear plastic disc with a cross scribed on it. Fit them both into a 12 inch PVC tube that fits your finder bracket, each at either end, and simply center the post/crosshair shadow onto the paper guide marks to center the OTA. You could even cut a side port into the tube and look in from the side to make it a "RA Finder" (mount the screen at a 45* angle - kind of like some LASER collimators). If you needed more "power" simply lengthen the tube (distance between the post/crosshairs and screen) as needed.

Conversely you could replace the post/crosshairs with a large "pin-hole" made from tinfoil and have a crude image of the sun on the screen to line up with the reference marks you made. See which system works best for you.

FWIW

TM

Not all that controlled but it would be interesting to have someone put a dollar bill on a fence-post at a dark site (before the sun set) and have a "bino shoot-out" with many different individuals.

Bet a few of the bino owners would not like the results, too!

TM

Alex,

I have had one for 3 years and the answer depends on what you want to do (like so many things in life!)

So, the answer is "Yes and No" ...

On the "Yes" side - for a new 8 inch SCT with a warranty it's a good deal *IF* you remember it's has a totally manual light-duty mount. You will get the same OTA as the other LX series have (including the well received long running LX-200's) but the fork arms are much thinner and lighter. Due to this fact the LX-10 is pretty much a visual scope by design. If you do want to start out on photo work maybe try some CCD work or guided piggy-back photos and it should be OK but if you get bitten by the photo bug you will want a better mount. Optical quality should be in the 1/4 to 1/6 wave range (pretty good but not in the league with a Tak or RC SCT). It's lighter (comparatively) than most other 8 inch SCT's so it's easier to take out the door and set up. It will also fit in cheap COSCO luggage (I did that and reinforced the sides) and is more "luggable" than SCT's on beefier mounts. You will only get the 35mm finder but it's not a big thing as you may want to upgrade to a 1X red-dot or do what I'm doing - piggy back a 80mm F5 as a "big" finder (a very common modification for 8 inch SCT types).

On the "No" side - The normal SCT gripes - some image shift, 33% central obstruction, cool down time, etc. Also, the standard field tripod is a pain unless you are about 5' 2" tall. I traded mine in for the adjustable field tripod within 2 months of getting mine. You can get a used one for about 150 here on AM and sell you standard tripod for 70 or so to recoop the cost. I have the HD wedge so I can't comment on that issue. For visual the vibrations stop in about 2 seconds maximum for me so it's fine for visual work.

Since the best scope is the one you use the most my considerations were light weight and general simplicity. The LX-10 is a very simple and relatively light SCT with few bells and whistles. Even with the set up involved the LX-10 seemed to me to be a kind of a "large" grab and go kind of scope. Also, since I tend to be somewhat of a minimalist by nature (and actually like hand slewing the OTA anyway) all the motors, batteries, and other collateral stuff did not appeal to me. But I do have the Magellan I DSC with object library to guide me if I feel up to plugging it in and setting it up.

That's my 2 cents - good luck!

TM

Alex,

There is a LX10 for $700.00 on the classifieds right now WITH the better (adjustible) tripod included. That's not a lot more that what the OTA itself would go for for the mount, base, telrad, better tripod and one EP.

Just a heads up ....

TM

I consider myself a reasonable, non-violent person (and know the Russian space program is having some hard times) but KILL IT, KILL IT, KILL IT!!!

Maybe the SDI (a.k.a. "Star wars") folks could use the big Pepsi signs for target practice ... or turn the hardware over to the Earth Liberation Federation (ELF) and let them have some fun (while killing a few H2’s and Escalades in the process, too!).

Seriously, just the screwing up the environment aspect of this half A$$ed crack-pot idea would doom it real quick. It's already been estimated that 100,000,000 (yes, Martha, that's 100 million) birds die a year in the US flying into lit up skyscrapers and radio towers. What would happen if this clown actually DID light up the night would make that number small potatoes (not to mention the light trespass law suites, and I'll be first in line!).

TM

I'm betting it's 12 inches (about 305mm) on the mirror (the corrector is a bit bigger than the mirror but the mirror is what will determine the "objective diameter").

If the FL is 600mm that makes it about an F2 system (!). Really fast! The central obstruction it about 59% so it WILL effect the contrast but this thing is SO big and fast it's almost off the radar as far as "normal" astro optics.

If it were mine Id first try is as an astrograph with medium (2 1/4 by 2 1/4 inch) or even 4 by 5 inch film. At 600mm the medium format file is like 5.5 degrees and the 4 by 5 inch down the line of 9 by 11 degrees ... if the optics were OK you could do some very nice wide-field photo work (probably what this monster was made for).

If you want to try this as a observational scope you might have to Barlow up the system to about at least F4 (2X Barlow) to use any standard EPs on it, otherwise the fast system will run over most production EPs. Of course, you could try to make an EP for is but the exit pupil should not exceed 7 mm and the is a power of (300 / 7 or) about 42 power. With a barlow (2X) that would be 1200 / 42 or 28mm or "unbarlowed" it would be 14mm.

At 42X this is only 3.5X per inch so the optical quality would REALLY have to suck to be noticably bad. You could get a nice WF EP (70 or 80 deg. AFOV) and make the mother of all Rich-field scopes out of it ....

Have fun!

Welcome to AM - hang around and make yourself confortable!