Louis D

15 hours ago, Deepblue12 said:

Thanks to everyone for their responses. I'm no maths whizz and whilst i understand the basics of vlaiv's explanation i think i'm after a more "rule of thumb" calculation.  

So i have a Celestron 127slt (1500mm Focal length) and 25mm, 15mm, 8mm Eyepieces and a 2 x Barlow.

if i take dannybgoode's  calcs then i have a theoretical maximum magnification of 254 and the nearest i can get to this would be using my 15mm and the Barlow (1500/7.5=200) 

That means my best option in optimal conditions would actually be to use a 6mm eyepiece giving me 250?

Fully understand that this isnt a hard and fast rule but are my maths about right.

 

The best way to go is to actually try each combination on the object in question to see which looks best to your eye.  Math can only tell you so much.  At some point, you need to experiment to verify the theory.

Yeah, the 35mm Scopos is a special eyepiece.  I may have bought the last of the remaining new old stock when I bought it from Europe since they showed as unavailable after that.

It is extremely pin sharp in the inner 75% or so of the field and not very much worse beyond that.  I mean really sharp compared to my other 32mm+ eyepieces.  Stars are just teeny tiny pinpoints.  Sometimes I'll pop it in on a rich star field just to soak in the view because its so awe inspiringly well corrected.  There's no field curvature and plenty of eye relief.  Given its 47mm diameter eye lens and ~17mm of eye lens recession (IIRC), it could have had much, much more usable eye relief.  I once screwed off the top cover with the eyepiece vertical just to check.  Sure enough, even with eyeglasses, it was very difficult to hold the exit pupil because the eye relief is so long, and there was no reference point to touch with my nose or eye socket.

The downside is that it is my second heaviest eyepiece (behind only the 17mm ES-92) at 37.8 ounces or 1072g.  However, if I balance for the ES-92s, it's a natural to use it as my finder eyepiece before swapping to them.

Here's the updated 32mm-42mm image which includes the 40mm Pentax XW.  I have returned again and again on different occasions to try to capture a better image, but they all turn out similarly, so I went with the one shown.  As you can see, it's not perfect to the edge by any means.  Even with the field flattener, slight curvature remains, but the camera lens has enough depth of field in my experience to counteract it, so that's not the issue.  It's mostly just residual astigmatism.  It's not bad, but it is there.

Yes, I forgot to mention I have a TSFLAT2 spaced 15mm in front of the 2" GSO dielectric diagonal to flatten the field.  Since I have no focus accommodation anymore, it was maddening trying to take in the entire field at once when vast portions of it were completely out of focus to my eye.  Younger folks might never notice the field curvature of a short refractor.

I have the Meade 5000 Plossl 40mm 60 degree version of the ES-62 40mm.  While it's exceptionally sharp in the center and almost totally devoid of field distortion, it is only sharp at f/6 in the inner 50% and falls off beyond that.  It has a 42.7mm field stop by my measurements, so not quite as wide as the Aero ED 35mm at 44.4mm.  For comparison, the Pentax XW 40mm has a 46.2mm field stop.  I'll have to check if I have an updated image that includes the XW.

Here's my comparison images of 32mm to 42mm eyepieces in an AT72ED f/6 refractor imaged with a Samsung Galaxy S7 camera:

Doing more filter research, it turns out my Minus Violet (MV) filter might have either a 420nm or 455nm cutoff and might also be referred to as a Wratten #4 Yellow.  Either way, it's not particularly useful visually with fast achromats.

There's also a Minus Red (MR) filter, or a #44A Light Blue-Green/Cyan.  However, it isn't really a true analog of the #12 Yellow (Minus-Blue) filter at the other end of the spectrum since it doesn't have a level pass band up to about 600nm.  It's more of an arch that cuts off spectrum on either side of a peak around 480nm and fully cuts off by 560nm, well before spectral red.

It's unfortunate that no vendor has stepped forward to purchase a new production run of the 40mm TMB Paragon clone (Aero ED/Paragon ED/Titan II/Paracor/Sky Rover).  The only change I would make would be to bring the eye lens up to being closer to the top of the upper barrel to make it more eyeglasses friendly.  Since the clone comes with a really nice twist up eye cup, why not?

The 35mm Aero ED would work well as a near widest field eyepiece if you can still find one in stock.  It's pretty sharp in the inner 75% of the field of view at f/6.  It gradually gets more abberrated toward the edge.

The 40mm Pentax XW works really well at f/6, but is quite a bit over your budget.

First off, what are you going to be using them in?  Assuming you want to avoid going over a 7mm exit pupil, you wouldn't want to use a 50mm eyepiece in a scope faster than f/7 and a 56mm eyepiece in a scope faster than f/8.

Here's a post on CN that gives the Barlow magnification equation.  You still have to work out the Barlow's focal length and the distance between the Barlow's optics and the eyepiece's field stop.

I've been using the GSO 2" 2x ED Barlow, which is sold under multiple other brands, for years.  It is very sharp and pairs well with the Tele Vue Panoptic Barlow Interface (TV PBI) to make a poor man's Powermate for use with wide field, low power 2" eyepieces.  There's a recent thread on CN discussing it.

The Zhumell brand was more or less discontinued in favor of the Apertura brand by Telescopes Plus a few years back.  It's still the same GSO telescope.

56 minutes ago, CCD-Freak said:

I like to use my AT60ED for terrestrial viewing with a 45 degree erect image diagonal.  The little scope is quite compact and has a very smooth focuser and crisp optics.   The AT60ED is often referred to at the "Tiny titan" I also use it for wide field imaging with the optional field flattener.  

Are you sure you didn't undermount that AT60ED just a bit? 😁

Here's an interesting web page that goes into great detail mixing and matching between high quality spotting scopes/eyepieces and astronomy scopes/eyepieces for birding.

8 hours ago, Stephenstargazer said:

Others might go the Dob route, great value but less portable.

I don't know about that.  I'd rather transport an 18" Obsession Ultra Compact any day over a 16" Meade SCT:

That's 90 pounds vs 318 pounds, not to mention how compact the Dob stores.  If you need tracking, there are lightweight EQ platforms for the Dob available.

I'm going to try adding a light blue filter I have on hand (it might be an 82A, I'll have to check) to the #12 yellow to see if I can block some of the spurious red without losing the yellow/orange part of the spectrum as with the green interference filter and without dimming the overall view too much.

I've been researching interference shortpass filters that cut-off at 600nm to combine with the #12 yellow to broaden the passband of the green interference filter while eliminating the unfocused red light.  None are particularly cheap and might be a bit small (1 inch) for 1.25" usage in stock sizes.

The #12 yellow already acts like a pretty good longpass filter with approximately a 500nm cut-off.  Unfortunately, there doesn't appear to be a Wratten equivalent for blocking red wavelengths.  I'm not sure what color the eye would perceive all spectral colors combined except for red.  I'm thinking it's sort of a teal blue-green.  None of the Wratten spectral graphs look like a horizontally reflected yellow filter.  I'm guessing it's an undesirable color, so no one ever thought to make a filter in that color.

Even with reflectors that don't suffer from increasing chromatic aberration at faster f-ratios like refractors do, figuring an f/3 paraboloid is much more demanding than figuring an f/8 paraboloid.  In fact, the f/8 barely differs from a spherical mirror, so very little parabolization is required.

I'd go with an ED refractor for daytime use.  CATs yield low contrast in daytime usage as well as really weird out of focus highlights for bird watching thanks to their central obstruction.  Non-ED refractors have so much unfocused violet and far red that the view is again low contrast.  Daytime features are much lower in contrast than nighttime features.  A ship on the horizon is much like a comet on the horizon at sunset.  It is very low in contrast.  You need a high contrast scope to pick either out from the murk.

2 hours ago, Stardaze said:

I’m not too bothered with the 3.5 at the moment, I don’t think it will get used much. 

I have one, and you're right, it doesn't get used much.  I tend to transition to my binoviewer at very high powers instead.  The 3.5mm XW is faultless, though.  It's just that with my floaters, two eyes are much better than one.

15 hours ago, badhex said:

Not as much room between the Pentax and the Morpheus 4.5mm as I would like but it's a bigger gap than it looks, and once the lid is shut it's nicely held in place by the top foam.

If you have a bit of loose P&P foam saved from this case or another case, just wedge it between the two eyepieces to guarantee they don't bump each other.  I do this with some of my eyepiece cases that aren't well organized.

It comes in handy to hoard those P&P foam bits in a grocery bag at the back of the closet for this reason.  I also sometimes use them to shim holes when a new eyepiece is narrower than the one it replaced.

34 minutes ago, mikeDnight said:

Very few observers ever really study an object at the very edge of the field, but centralize it.

Most folks who use nonmotorized alt-az mounts allow the object to drift from edge to edge to get uninterrupted observing time.  At higher powers, wider fields of view become critical.  Trying to use a 30 degree monocentric at 300x under these conditions would be maddening.  However, using a 110 degree HWA is quite doable.

Most of the Morpheus range actually measure out to have 78 degree AFOVs.  The lone exception is the 17.5mm at 74 degrees.  The ES-82 range have measured AFOVs of between 80 and 85 degrees, so only a bit wider in some cases.

The eye relief is much better with the Morpheus if you have astigmatism in your vision and need to wear eyeglasses at the eyepiece.

The Morpheus may be better corrected to the edge.  Some focal lengths come close to Delos and XW levels of correction in f/6 and slower scopes.  The ES-82s tend to have slightly poorer correction than their Nagler equivalents except in slower scopes where the difference is negligible.

Definitely go with a visual back with 2 thumbscrews.  The fit is so much more secure than with just a single screw.  3 screws doesn't buy you anything, so avoid them.

Look to see if the adapter is already on your 127 Mak's rear port.  If it does, it can be screwed off to verify what I'm saying if you grab it with a rubber jar lid grip to avoid cutting your fingertips on the threads.  The factory did not change the rear port opening or thread size, they just included the SCT thread adapter with newer Maks.

I have one 127 Mak that I had to buy this part to bring it up to SCT thread size, and a newer 127 Mak (for my adult daughter) that came with the exact same adapter already installed.

Have you tried threading a 2" SCT visual back onto the existing rear threads to see if it fits?  My daughter's Mak came with a 2" SCT visual back from the factory.  Perhaps yours came with a 1.25" SCT visual back.

On 15/12/2021 at 18:44, johninderby said:

Maks and SCT have corrector plates on the front so you can’t use a simple fan. You can use a specialist cooler  that is inserted into the scope through the focuser and circulates air through the scope and blows it back out. 

https://www.firstlightoptics.com/misc/asterion-cooler-cat-for-sct-maksutov-telescopes.html

I’ve had both maks and SCTs but have now moved on to a Classical Cassegrain which is open at the front so cools down faster and no dewing problems. Also uses a proper crayford focuser and fixed primary instead of the mak and SCTs moving mirror type focuser.

Perhaps you can explain why the 8" CC at 18 lbs is about the same weight as the 180 Mak at 19 lbs when the latter has both a thick meniscus corrector and primary mirror moving hardware for focusing of which the former has neither?  I can't imaging moving from 50 sq. in. of mirror to 64 sq. in. of mirror adds as much weight as a 180mm+ meniscus corrector and mirror moving hardware.  Is the CC focuser incredibly heavy?  Are those tube baffles incredibly heavy?  Is the secondary support incredibly heavy?  Do all the differences simply add up to the same weight?  It just seems like the CC should be sooo much lighter, not just a single pound lighter, than the Mak.