Posts Made By: Thomas Dey

That sure seems terribly suspicious, but I've had no direct experience. Would think all the tolerances would be self-aligning provided the scope itself is good. What is the signature of the poor alignment? (I have equivalent Meade-to-Meade f/6.3 "Reducer/Flattener" and had no such problems). Someone with your same setup may shed light on this. Tom Dey

I agree with Pete. Although Saturn looks plenty bright thru an eyepiece, it is WAY dimmer than the moon...so crank up the gain and/or integration time. When I'm seeking and framing an object, I intentionally overexpose by a LOT and then adjust down to actually collect images. Good practice would be to image the moon and then swing over to Jupiter or Saturn to see what settings are needed...focus would of course still remain the same. About the only cams that won't lose dim objects at near-video frame rates are those incorporating Gen3 intensifiers! Tom Dey

The general rule of thumb used to be to go half the max weight capacity for long EFL "high mag" deep-sky imagery. That, and RA gear as big as the aperture. I know my extremely beefy 12.5-inch Cave Astrola was a nightmare to image with until I replaced the fiberglass tube with custom metal reinforced tube AND retrofitted a Byers 11+ inch RA drive, new zero-backlash Dec drive, off-axis guide splitter and SBIG autoguider. That gave me RMS guiding accuracy of 0.5 arc-sec RMS and never wandered more than about 1.5. But back in those days, DS film-based single continuous exposure times were 2 or 3 HOURS! EFL was ~2000mm. The guiding EFL was barlowed to 2500mm with a very mild custom barlow. That might seem totally nuts now...but was needed back then. Things would certainly be far more forgiving now with stacked, far shorter CCD exposures, etc. But I still think the consul to underload the mount by a lot will make imagery far less frustrating. Tom Dey

Interesting! I had Coulter 13.1 and 17.5 Dobs when they 1st came on the scene and enjoyed them immensely. Now using a (GOOD!) old Coulter 29 (mirror in Astrosystems-like mount)...recoated and decent imagery to 500X. I never realized they made refractors. Tom Dey

Agreeing with Roland here. For a distortion-free eyepiece, the AFOV is 2 arctan(stop/2/efl). If distortion IS present, the field can "look" bigger or smaller...but that's sort of cheating, because distortion IS change of focal length with field! With some binos (and especially bino-viewers) the prisms, etc. can further restrict available vignetting-free field. If an eyepiece has an Internal field stop between lens elements, the effective stop size is how big it looks from the bottom. The size of the focuser hole indeed determines max potential field. Tom Dey

God - that thing is still on display there! It is indeed true that Rochester is home of Bausch & Lomb, Eastman Kodak, Xerox, Rochester Precision Optics, U or Rochester’s "Institute of Optics" etc. I examined that piece and it's just a tube thing with a flat disc of glass on the front. I remember wishing the artist had at least consulted a local optics company for something a bit more lensish. Tom Dey

Magnificent, Roland! I especially appreciate your tuning of processing and display parameters. You have pulled the max info and aesthetics. So far ahead of the film work I used to do years ago. Also nice that we can enjoy La Luna as a target that happens to be orbiting earth waiting to be imaged. And as we have confirmed, the craters are sort of fractal in their distribution - loaded with structure at all sizes from humongous to miniscule. Well...I'm going to stare at it some more! Tom Dey

Glad to hear it's working. I've bought a LOT of stuff on Astromart and happy with it. But on some few ADs over the years I've immediately offered full asking price (SOMETIMES EVEN MORE!) and just heard crickets day after day and the ADs hang in there --- could never figure that out! When I DO offer it's nearly always straight-up without a zillion questions, conditionals or low-balls. But I always ask the seller to let me know "either way" so I'm not left wondering. That near always works out just fine. "Sorry, but I already sold it" is appreciated. Also noticed that some HOT items sell almost IMMEDIATELY (popular eyepieces. etc.) Especially coveted items where the manufacturers are back-ordered. I get amused by the auctions (without reserve) where a starting bid of $1 hangs there. Nother amusement is where a seller with no history asks like DOUBLE what the going used price is. A couple of times I have even given a seller a courtesy reply that they are asking MORE than NEW in-stock price from a reputable dealer! The archived available year's history is extremely useful when pricing an item to sell (or buy). Tom Dey

The transition from film to solid state is fascinating. "Full Format" film was most always 24x36mm and the 1st CCDs were microscopic, coarse and obscenely expensive. The chips gradually got bigger Bigger BIGGER and cheaper Cheaper CHEAPER...until now "Full Format" chips with magnificent performance are available in what emulate the old high-end film-based SLRs. So suddenly those old, magnificent lenses are the Perfect Match again! I have a nice compliment or great old minty Olympus (manual) lenses, including the coveted 100mm F/2 that cost $$$ originally and the very best Nikon. The greatest irony is that Kodak pioneered the very best chips (their KAF series) still preferred by high-end users today (for uniformity, low noise and freedom from defects). Yet as film precipitously faded from the scene...the company all but folded. I worked for Kodak and witnessed uncountable rounds of layoffs (luckily evading the shrinkage). Fortunately, I was on the government contracts side of the business, which had gone solid state WAY before the commercial market did. Tom

Full ap filters on the larger scopes (even just for white light) suffer poor wavefront. Also, such filter will squeltch the H-alpha so you wouldn't see anything at all with the combo. H-alpha generally requires very slow feed at the filter itself - Daystar recommends f/30 or slower. This is why the red off-axis ERF filter up front is used on SCTs - it both evades the secondary obstruction AND slows the feed to f/30 or slower. The dedicated solar scopes with internal etalons like LUNT, even though the scope itself is ~f/7, uses telecentric optics downstream so the light passing thru the etalon is slower (much slower) than f/30. Front-mounter etalons are operating at object-space equivalent of f/120 (étendue of the Sun). Short answer though is to stick with the standard COMBINATION of filters for line spectra (H-alpha, sodium-d, CaK etc.) Otherwise it could risk damaging your eyes! For white light the dedicated "visual" Solar ND up front is safe as is the Herschel Wedge + polarizer (like Lunt makes) when coupled to recommended refractor f/5 feed or slower. I have found that the LUNT wedge has MUCH better wavefront than up-front ND. Always use the filter COMBINATION recommended else risk eye damage. Final thought: I found that amending a green GLASS (Wratten 56?) filter + ND "moon filter" to the Herschel Wedge gives the BEST imagery when using an APO (Genesis) refractor. I think that is because the naked CCD sees IR and the apo is designed for visual spectrum. The green glass both rejects the IR AND is quasimonochromatic so takes stress of the performance of the chromatic correction of the lens. The IR manifests SEVERE chromatic and spherochromatism if allowed to get to the CCD. Sorry for the rambilng! Tom Dey