Andrew_B

3 hours ago, johninderby said:

I’ve found very little to choose between the Steeltrack and the FT crayford except the Steeltrack will handle more weight. The FT maybe edges out the Steeltrack by a little bit.

The FT R&P focusers are my favourotes though but not cheap. £££££££ 🙂

What are the pros and cons of R&P versus Crayford? I've got a 2" Crayford FTF on the way but I didn't see a R&P option in that size - not that it matters and I'm sure either would be more than good enough for my needs.

On 13/09/2021 at 21:56, vlaiv said:

Again, I can't really tell if you do.

Pixel wise, ASI485mc and ASI178mm are very similar - 3840x2160 vs 3096x2080 - you are really only getting about 800px in width and 80px in height.

If you want larger sensor just for the FOV - then with above trick you can extend FOV of ASI178 to larger size and still have 3096x2080px (mind you - you could do some hybrid approach when doing mosaics - if you put 3x3 panel mosaic for example - you'll end up with roughly 9000 x 6000 px - you could bin that x3 as described above or maybe even x4 and end up with 2250 x 1500px image in the end - gaining a bit more SNR in the process - not many people have displays to show 2250x1500 without resizing).

If you want ASI485 for "speed", well, we need to do calculations - 2.9µm pixel size with 1/4 getting red, 1/2 getting green and 1/4 getting blue vs 2.4µm some sort of LRGB imaging with full pixel usage - for example you could do LRG. You really don't need to do full LRGB to get proper color - since we are using luminance that collects all three color bands at the same time thus increasing SNR for given imaging time and since luminance is more important visually then chrominance and since we need only 3 components to get color - you could do something like 3/4 of lum and split 1/4 of time between Red and Green.

Which one would be faster in that case, Color camera or mono + filters? It is very hard to tell if we don't do the math (and even then we would need exact color matrices in order to calculate things properly - that is if you want true color rendition).

If you want ASI485 for "novelty factor" - time to get new gear, then maybe consider getting cooled version of some camera instead?

There are cheaper and better alternatives as well. How about APS-C sized mirrorless camera? If you mod that by removing IR cut filter - you'll get very good 6000x4000 large sensor camera that is essentially the same for DSO (it won't be as good for planetary).

We touched up on that subject in another thread (might be interesting read):

 

 

I second the suggestion of a modded mirrorless camera. You can pick them up secondhand for very little money compared to what a dedicated astro camera would cost. I got a full spectrum converted 24MP Fuji for just £180 and the performance is very respectable even when shooting narrowband.

59 minutes ago, Deadlake said:

That’s around £6500 in today’s money, I guess hard sell in triplet world of today?

Tak doublets have a pretty devoted following and a 5" fluorite doublet would probably sell in reasonable numbers, not least because just about everything else available at the high end in that aperture range are triplets, quadruplets, and whatever else aimed at the imager. Astrophotography drives most of the market but there's still a decent number of visual observers or people who do both and enjoy the convenience of a fast-cooling and lightweight scope.

I've just had a look at an old Tak advert from 1990 and the FC-125S was selling for £5,400 back then which is the equivalent of over £12,500 today. Even high end astro gear is far cheaper than it used to be.

3 hours ago, Ags said:

This thread makes my head spin. With every post I hear about new exotic compounds that I never even imagined existed. But every option gets shot down. We are the species that put some of its members on the moon right? How hard can it be to keep some threads unlocked?

What about ordinary items I might find around the house? How about vaseline? Shoe polish? Actual graphite from a pencil? Extra virgin olive oil? Goose fat? Skin cream? 😀

I've used both vaseline and candle wax to grease threads and they worked well enough. The reason I chose them was because they were immediately available and I know what's in them so there shouldn't be any nasty surprises and they ought to be relatively easy to remove if they end up in the wrong place.

Stuff like molybdenum disulphide grease or graphite grease might do the job well but if they get on your hands and then on your clothes or furniture then it's going to make a mess.

3 hours ago, John said:

Well said @Stu

The scope that has given, and continues to give, me the most from the hobby is my least expensive and probably the most compromised as well !

 

 

If a scope gets you out observing and you enjoy it then it doesn't matter what it cost or how close it gets to optical perfection.

I suspect that people who spend their time worrying about what they can't see because of the limitations of their scope will never be satisfied with what they can see.

33 minutes ago, dweller25 said:

My FS128 is F/8.1 and IN FOCUS it is colour free, so maybe a modern lens design could be better ?

Using a wide air space can give better correction with a given pair of elements so that might be an option, but it would mean a larger and heavier scope that might be a bit more prone to losing collimation.

That said, the old FS-series were a lot bigger and heavier than their equivalent modern FC-series scopes so perhaps a lightweight but highly corrected 125mm doublet could be a viable option.

8 minutes ago, vlaiv said:

Don't mind me, I was being somewhat provocative with that post (trying to be half provocative and half funny).

But there is a point to it - maybe not that exact SW model - as you yourself pointed out - people do like nice Strehl figure, but comparing two different aperture scopes with different Strehl is another matter.

On purely optical side of things - larger aperture diffraction limited and obstructed scope can outperform smaller clear aperture with perfect figure. In practice it will also depend on atmosphere of course and target, and observing conditions, and there are also personal preferences of course.

 

It's okay I could appreciate the humour. 😁

Like you say there's so many factors involved like presence and size of an obstruction, cool down time, convenience of different designs, local seeing, etc, etc that what counts as a good scope will vary enormously from person to person. Sometimes people get a bit too focused on judging things in terms of easy to compare numbers rather than more qualitative factors and want a single easy answer about what's "best" that they can apply universally.

7 minutes ago, jetstream said:

I think the f ratio should be over f12 for this at 6" aperture? But yes, the likelyhood of getting good 6" f8's and 8" f6's is really high. I guess thats why the 6", long fl newts are called "APO" killers.

I think I must have read that info somewhere on telescope-optics.net and this page has the formula for the minimum focal ratio at which a spherical mirror gives acceptable performance as the cube root of 90.15 multiplied by the diameter in inches. For a 6" mirror this would be F8.15 so a spherical F8 optic should be close enough to be good but I'd imagine they'd parabolise it anyway.

6 minutes ago, vlaiv said:

Maybe because it will be outperformed by this:

https://www.firstlightoptics.com/reflectors/skywatcher-explorer-150pl-ota.html

😈

I bet that's a really impressive planetary scope and a good 6" F8 mirror is easy to make and apparently should give decent performance even if it's left with a spherical figure.

Mind you, you couldn't pay me to own a Newtonian, they're just not my cup of tea.

1 hour ago, Deadlake said:

How much was the FS128 when it was out, relative to a 100mm Takahashi? I suspect at 130 mm the TOA is popular as one of the best imagining scopes at that aperture and that's where the market is.

Note:

Takahashi should supply a lens report, LZOS and AP guarantee a minimum tolerance. 
TecnoStar also provides a minimum lens quality on their 130 mm model as well.

LZOS provide test reports because they're a contractor selling components to a third party. They're not doing it for the benefit of the end user even if the people buying the completed scopes do love those Strehl numbers.

Even publicising the minimum tolerance isn't straightforward. Is it referring to peak monochromatic Strehl or minimum across the entire visual spectrum and how much difference would it make in the real world anyway? Ultimately a good test report is worth nothing if you don't like the view through the scope and I don't need a test report to tell me whether I can see false colour or if my scope delivers a perfect star test.

4 hours ago, vlaiv said:

Yes, except that is for 462 model so really marginally better than nothing

That's annoying. I was sure that was for the right camera and it was one of the first results when I searched for reviews of the 485C model. The perils of skim reading!

I notice the 462 uses 2.9 micron pixels and has very similar characteristics - perhaps the same basic pixel architecture so the 485 might in practice be like a scaled up version of the 462.

QHY launched their version using the same chip earlier this year as the QHY5III485C. Only found this one review but it's better than nothing!

3 hours ago, gorann said:

If you have taken a dark image with an ZWO ASI071MC and stretched it you will see a clear "amp glow". The 071 comes with the older generation Sony chips, the newer ones sold by ZWO that do not show "amp glow" are the 533, 2400, 2600 and 6200. The 183, 294, 071 and 1600 all have amp glow, but it is easily handled by subtracting darks.

The starburst glow (or sausage glow since I like that name!) doesn't seem to be a problem with DSLRs so presumably cameras based on the sensors from consumer cameras should be free of that glow compared to those based on chips intended for machine vision and surveillance cameras.

Not wishing to derail the thread but does anyone have a link to a good guide for how to do things like calibration frames etc to deal with amp glow and fixed pattern noise in lower cost CMOS cameras? I want to try some deep sky imaging with my little ASI178MM (only used it as a guide camera so far) but the workflow is clearly rather different to what I'm used to.

1 hour ago, Deadlake said:

That’s slow compared to a 130 mm triplet I own, Takahashi make you wait for the good views…😃

Is you triplet using an oil-spaced lens?

6 hours ago, Deadlake said:

Ageema already make them, however a long wait time and not that much lighter then many triplets.

Only produced in small numbers as well. They look superbly made to the point of being over-engineered although the weight does kind of remove one of the big selling points of having a high quality doublet in the first place.

In theory one of their scopes would be an option for the OP but waiting times and no availability secondhand pretty much rules them out.

3 hours ago, Highburymark said:

Yes - it’s a DC with the green ‘spacer’ section removed (shown at side) as I needed the extra light path for binoviewing. 
The size doesn’t stop me from going out, but whereas before I had two refractors of similar size (85mm and 100mm), I now have greater distance (between my TV85 and 120mm TSA) - so if I want a really short session I grab the TeleVue, and for longer sessions, particularly in good seeing, I’ve got the bigger aperture.
I know I won’t be able to handle the TSA for ever due to my bad back. I’m hoping I can get at least 5-7 years out of it before it proves too much. But that might happen far sooner.
I am 100% sure that I will then go back to a light fluorite doublet - almost certainly an FC-100DZ  (or an FC-115DZ would be nice if anyone from Tak’s product development department is reading). 

You should drop Tak a line about wanting a larger fluorite doublet. I'm sure they're aware that there's demand for one but more evidence of that can't hurt and even the biggest companies do pay attention to customer feedback - I once emailed Apple about overly aggressive noise reduction algorithms in their smartphone cameras and they came back to me about it asking for more information and example images.

3 hours ago, Fedele said:

Many thanks...

wich Fc is this

Thanks for the first-hand response. Do these larger sizes discourage you from using it compared to the FC?

Looks like it's an FC-100DC with a Starlight 2.5" Feather Touch focuser. Hadn't realised just how compact it is compared to the TSA-120!

On 08/08/2021 at 11:28, garryblueboy said:

Not quite an LZOS but not far off An Astreya Quadruplet Russian optics by Andre Strakhov 001 formerly Intes micro Tube and design  TMB-APM -Mathias Wirth Kruprux tube 

That's a fantastic looking scope although looks like it must weigh a ton!

What design is it using to have 4 elements? Is it a flatfield Petzval or something else?

The TSA-120 would tick a lot of boxes although it's obviously at the lower end of your aperture range and may not be a big enough step up from your current FC-100. Never had the pleasure of using one myself but I know some of the members here own or have owned one. Stepping up to the TOA-130 would get you optics that are about as good as it gets but you'd have to find one on the secondhand market to be within your budget.

An APM/LZOS scope might be an option but it would be the same situation as the TOA-130 of you needing to find a pre-owned example.

@johninderby - just wanted to let you know that I picked up a cheap but surprisingly solid Svbony dovetail saddle that does the job brilliantly, so thanks again for your help.

My ADM dovetail was ever so slightly too wide to fit it though so I took a file to the saddle and after removing probably less than a mm of metal it's now a perfect fit.

4 hours ago, davhei said:

I thought so too and just this afternoon finished picking and plucking to fit my travel/grab and go setup into a Peli 1525 case. Nice size that swallowed an 80mm f6 refractor, diagonal, three EPs, barlow and filter with room to spare. Perhaps for a fourth eyepiece or something.

Slightly apprehensive regarding air travel. Like you said, it is just below or just over carry on size depending on which airline you choose. Oh well, I’ll cross that bridge when I get there.

I’m sure it will work well for carrying necessities for garden sessions and stowing in the back of the car for family trips where a bigger dob would take too much space.

Sorry, this was supposed to be a non-Peli thread but there you go. To stay on topic I’ll add that I use an orange Nanuk 923 case for eyepieces and other kit when out with the dob. Great case, well built and sturdy while cheaper than Peli.

 

That looks a really good setup - nice and secure with loads of protective padding around everything.

As far as I can tell the Peli 1525 should be okay for carry on luggage on most mainstream flights with exceptions possibly if you were travelling by light aircraft somewhere. It was other makes of similar style cases that seemed to have loads of models that were almost the right size but which would be a bit too deep or too long for me to be confident that they'd be allowed onboard.

Peli cases aren't cheap but when I think about the cost of what's going inside I'm not as bothered about paying a bit more to keep it all safe. I wouldn't just use it for holidays either because I'd take it with me when I wanted a little scope to use while I was out doing some astrophotography from a dark site. I ended up laying an outline of the internal dimensions of the case on the floor and then experimenting with different configurations of scope and accessories to see if I could fit a useful setup in the one piece of luggage and that showed it would do the job nicely.

33 minutes ago, Louis D said:

Then how about starting with a true carry-on sized rolling case and then adding the foam or dividers to it?  It's much less likely to receive unwanted attention in an airport terminal, and it comes with wheels and a handle to make transport easier.  Check thrift stores for used ones for cheap.  If it's just a small scope, you can probably pack it with your clothes in a regular carry-on since most airlines only allow one per passenger.

That's a good idea. Even expensive foam is a lot cheaper than a new case.

If I was taking a scope abroad I'd probably have it and a few accessories in its own carry-on case and then put the mount and anything else that was fairly rugged in with my clothes in a checked bag.

10 hours ago, Tiny Clanger said:

Yep, Ill second that, the cases are good, but I suspect while some (fareastern) sellers base their prices on what the case costs to make , others look to peli !

I've bought a couple of maxbright cases, one showed up as a suggestion after I got the cheaper festnight version, The maxbright was orange (vs the festnight's black) and for a short time the orange maxbright was £20 , so I had it ! Turned out to be sent all the way from Italy, which is perhaps where maxbright are based. The cases are very similar, small, but capable of taking 9 (or maybe more) eyepieces standing up, and some filters etc.The festnight came with cubed foam, the maxbright with solid (so not as advertised, but I wasn't sending it back !) . I use stiffer closed cell foam anyway , and cut neat circular holes for the eyepieces to stand in with a bit of sharpened metal tube .

I do enjoy the amazon reviews which say the item was smaller than expected , when the measurements are clearly given ...

That orange case is smart looking and not a bad price. Less likely to fall over it in the dark than a black case as well.

I've also been looking for a travel case for my little scope and the Peli 1525 seems to be the best option but it's quite pricey. It's surprising how many protective cases are almost carry-on sized but are ever so slightly too big in one dimension.

4 hours ago, Geoff Lister said:

+1 for Copper Slip.

WD40, or "Water Displacement, 40th Formula" is not a long-term lubricant, but works as a releasing agent and temporary surface protection. I have had my trusty tube of Copper Slip for several decades, and I would not expect to fit any steel-to-steel fixings without a thin film. I have also used it, in bulk, when replacing steam loco boiler washout plugs - without it, the high-pressure water and thermal cycling, can make them difficult to remove.

Geoff

WD40 was never designed to be a lubricant. From the outset it was a corrosion-prevention compound for the aerospace industry that was first used by Convair to protect the thin stainless steel skin of the Atlas ICBM!

5 minutes ago, wulfrun said:

I actually have one that I've used for a while, in an f5 and an f8 reflector. I'm sure it won't be as good as a premium EP but actually I don’t notice anything particularly bad to criticise it for. For the price, I think you'll find it works quite well.

That's good to know. I've got an Astro Essentials 20mm Plossl which gives a great view in my 60mm and I wanted something a bit lower power that wasn't too big and kept to a 1.25" fitting. Doesn't seem much point pairing a tiny lightweight scope with a huge heavy eyepiece!

Low power eyepieces give a lovely 3D view with that scope so I'm looking forward to trying it out. For £23 including delivery I'm not expecting spectacular performance, but simple eyepiece designs like Plossls seem to be fairly decent even when they're cheap.