GTom

Back to the mirror topic, I'd be interested on blank suppliers. The €1000++ per blank doesn't sound very encouraging.

1 hour ago, Cosmic Geoff said:

This post may provoke howls of rage and derision😀 but, why construct a massive Dob when with EEVA you could see equally faint objects using a scope of a fraction the size and bulk?

Using a 102mm achro refractor for EEVA I found that I could image in near real time fainter objects than I could see with an 8" SCT. 

No rage from my side at all, use that EEVA with a 24" Dob! I am actually seriously thinking on 1-2 minute subs deep sky photography.

Quotes started to arrive in my mailbox, apparently the basic budget for 24" mirror making will be closer to €2500 than to 2000, main expense being the €1500ish blank.

8 hours ago, jetstream said:

Yes, its nice to see a magnitude gain on stars between aperture increases IMHO- it will be hard to gain real benefit in an aperture jump from a 20" unless going to 28"-32" . In my case a 36" would be a nice increase.

Just my thoughts.

Full magnitude jumps are of course nice. It boils down to the additional investment you have to put in both work and $$$.

My position is easier, the biggest thing I got is an unused GEM mounted 12" in a steel tube on a dead mount - not going to return to that scope. Transportability and total weight is worse than a modern 20-24" truss Dob or a c14... I need to determine the right entry point in this world. This would be the largest scope which breaks down to less than 25kg/55lbs components, and a carefully designed, thin-mirror 24" seems to sit right on that limit.

20" is readily available off the shelf "cheap" from mass production (ES, Skywatcher), but I don't like the reviews I keep seeing on them AND of course the affordable ones weigh as much as a CF construction 24". Latter is a steep, 4x jump in price.

3 hours ago, Ships and Stars said:

I would if I could! That's a huge amount of money. I'd go for a Star Structure dob with Lochwood optics. Make it a 32" f3 please!

Indeed, 20"+ pricing is mostly guesswork/custom request the €3k/20" starting point doesn't even work there, because no mass producers like Orion will give you even a 22" mirror. E.g. Zambuto costs 50% more. There is a maker in Bulgaria, Astroreflect, their mirrors are sold by TS below Orion pricing but even a 20" is a custom order for them, I wouldn't wait months until they figure a 24" amidst piles of routine work - and pay a €5k-ish price...

Quote

Oooh I think it will take me a lot longer than 50 hours to get anywhere. I'll start with an 8" or 10" then do a 16" then see if I can go bigger.  I've read that over 16" things start to get really difficult in a hurry, even some professional mirror makers struggle with figuring large mirrors, the bigger the trickier. Before I start working on one, I want to learn how to test them first. Still lots of reading to do, just picked up this book below. I love thinking about it though! I think 25-28" is perfect for what I'm looking for. Larger than 28" and I will need a trailer behind by van or park it at a friend's farm. I'd be thrilled with something in the 24"-28" range someday.

Afraid so... I don't count the research/reading/ordering part - I can do that quietly anytime, only grinding-polishing with the aid of a pre generated curve. I am a bit flexible, but have to be realistic, 100+hours on the glass would mean no scope for 3 years.

I'll go trough Rustypsplit's thread on his very first grind, a 14".

Went with the mirror discussion to your mirror topic

Joining the club with big-mirror ambitions too :), unfortunately with no mirror making experience. Watching a dozen mirror making videos and reading reports, I am tempted to grind a 20-24" piece. I see the cheapest decent 20" ready made mirrors this side of the pond sell for about €3k (TS), a grand more if you want (and I do want!) a thin design. On the other hand, grinding has costs too. I am asking around for blank costs, this one seems very affordable, about half the price I've seen elsewhere!

Problem also with bigger mirrors, that you might want to build your own Mirror-o-matic, which directly adds to the costs as this is a single-mirror project. Doing my homework on the figures, I'll go ahead with home grinding if I see the total cost for a 24" mirror will stay below €1500 AND 50 working hours starting with a pregenerated blank. This includes the grinding of a 12-16" practice mirror if it's absolutely necessary...

2 hours ago, Ships and Stars said:

The small mirror blanks are expensive, but as you go up they get much cheaper and I don't know anyone who lists prices for blanks that large.  The curve generation is sold as an option it appears.

Found this German source, prices listed until 20" which costs €360, they do more on order.

6 hours ago, Ships and Stars said:

I came across this website after asking around for large mirrors. Definitely agree on the Italian styling on the dob there! Did you see they sell up to 32" mirror blanks with the curve generated!! Price isn't too bad either. 

Interesting! I wonder how much work a pre-generated blank would save to justify a 4x higher price compared to a normal blank? Maybe could get away even without making a turntable...

8 minutes ago, Ships and Stars said:

Thanks Gerry! It's been a handful. From Dec 17th until three days ago my wife and newborn daughter were in hospital twice with only a few days at home in between due to complications and a chest infection for the little one right out of the starting gate - that was touch and go for a bit. They are back and resting comfortably and our daughter is alert and I dare say happy most of the time. Hoping by next new moon I'll be able to at least get away once they are asleep to my dark sky site and return before sunrise (I honestly sound like some kind of vampire now 🤣). Just need the weather to hold. We've had four really clear nights here lately, high humidity, but lunar with the 8" has been my only option. Hope to file another DSO observing report soon! I'd like to turn my attention to more galaxies now after reading your last report. And play with binoviewers on the brighter DSOs of course!

Sorry for going off piste with the thread GTom! Go for the big scope second-hand! 

No problem at all :). Wish the family the best of health and good chances of observing. I am doing a little research at the moment on mirror making, but 20"ish is huge. Got many cloudy days here though, but still, likely a second hand scope would make the most sense. Fortunately more and more big ones are sold in Europe, Taurus, Explore Scientific, etc...

Thank you for the reassuring report! I am also looking forward to get a second hand scope (or build one myself). I will give it some thinking and of course careful testing why it is being sold. Haven't saw bad mirror reports on the 20" so far.

2 hours ago, garryblueboy said:

A Takahashi or Astrophysics cost 10times as much as a Skywatcher but you don’t see 10x the detail nor do you in an obsession see twice the detail so what’s your point it’s what you see at the eyepiece not what you read on the net that maters why not get yourself an obsession then with a Zambuto mirror and you won’t have to worry about the above simple 

You don't have to go as far as Tak or AP to get a mirror that doesn't fall out of collimation, doesn't delaminate and at least diffraction limited. Apparently vendors are shying away from giving replacement units on customer complains, they rather refund...

I am not 100% sure about that 10x details question in very good seeing (where it is worth to do planetary work anyway) between a decollimated, lambda/2 optics vs a decent lambda/6 orion kept in a good cell. I am not a quality snob (alright, a little bit), but there are some BASIC expectations towards a product which costs multiple thousands of $/€.

Or just turn the question around: apparently the optics is about lambda/2, mechanical quality is a weak beta version. As an absolute NOOB in mirror ginding and with little (but existing) experience in OTA building, could I produce the same quality? Very likely yes and the overall budget doesn't seem to reach $2k.

52 minutes ago, garryblueboy said:

Try reading the positive reviews for a change instead of the negative there’s good and bad in everything there are plenty of people happy with there mass produced scopes  they just don’t all write reviews on them 

Right, there are good scopes too, but price is very much connected to quality. No wonder that an Obsession UC costs twice as much.

Anyway, I am listening, anyone measured 0.90+ Strehl, stable collimation after a year of use?

2 hours ago, garryblueboy said:

2nd gen 

I am close to give up trusting any mass producers and thinking on building myself... We are in the 21st Century, still advanced materials (CF...) are nowhere in mass pruduced scopes.

4 hours ago, garryblueboy said:

Yes it was pretty good really not in the same park as my Zambuto was but still very sharp and with quality eyepieces and paracore no coma or distorted views I read there were problems with the early ones but the later coned out mirrors get great reviews 

There are very poor test results in the topic I've linked with scopes purchased in 2019. They might still be older models though. However, even a half-lambda quality mirror will give you details in that huge size, whereas the user might associate any defects with atmospheric effects.

Also found this: the primary is simply not supported adequately. 

1 hour ago, garryblueboy said:

To be fair they are not that bad my one was fine and for the price great value I’d say it was the best truss pole one I’ve owned it is a beast though and although can be set up by one person I’d recommend two the GOTO worked flawlessly I purchased mine from FLO in August it was there demo model so had had a few things sorted it does break down into small transportable pieces the mirror is quite stunning on these for what I paid I was very happy 😃  

Have you done a star-test with the mirror? I see zoning and other issues reported by more than one user.

Looking at the SW 450p 458/1900, does anyone have experience with a relatively recent (less than 2 years old) model? This review doesn't sounds very encouraging.

I was looking at a second hand unit which the owner wants to sell after 6 months of use. Now I know the reason...

The offered price is very attractive though, about mirror price. I will do some more research, what could be healed, but low quality metal (Corrosion? Flexing??) is really bad news.

Reviving an ancient topic I wonder if anyone has long-term experience with the TS EQ platform, especially some deep sky photography?

I am interested if a dual-latitude version would be possible, 28 AND 45 degrees. I intend to travel with the Dob, and those are interesting for me. Alternatively I wonder if latitude can be adjusted with e.g. a fixed angle wedge, shifting the range with 20 degrees??

The Geoptik is still half the price compared to the Tom O platform, I'd count it affordable if it checks all the boxes. Problem will be with all their plaform the Latitide on the Canaries where I go quite often (28°N).

A horseshoe type could work, that needs DIY and good carbon fiber skills/parts to keep the weight low.

I am thinking on astrophotography with a reinforced/DIY upgraded 16" travel Dob, 3-5minutes subs. Seen that the Tom O' dual axis platform does exactly that but got two problems with that:

#1, price: costs more than a GEM capable to carry a 16" Newtonian (CEM60). I know there are stronger, more expensive mounts out there - anyway, 2000$+ is beyond my budget.

#2, fixed latitude. The scope is a travel Dob which I intend to fly e.g. to Namibia - unfortunately I don't live South enough to be on its Northerly counterpart. Neither I want to pay TWICE the $2k+ price tag.

#3, polar alignment: no polar finder, better PoleMaster no deal. In 2020 the maximum time I want to waste with PA is 5 minutes. I have two trackers meant to be used with small telepoto/standard lemses: both came with polar finders.

Any recommendations? I am also open for DIY, however need a decent low-latitude design first.

On 30/08/2018 at 04:47, rigradio said:

This is the Tamron version -> Andromeda

You will find Tamron vs AT65EDQ images on that page also. 

Website vanished unfortunately, is there an updated link? I have a sigma 150-600 Sports and wonder if it is up to the standards of a 90mm triplet. The only reference I saw was the Moonshot above, which is far much sharper than mine, probably I was shooting trough a very turbulent atmosphere from our balcony.

I have a Fornax lightrack mount, with a counterweight I could use it, but I need to figure how to use filters with my nikon z6 (no clip filters on the market).

I have to travel long for dark sites, the sigma packs significantly more compact than any 90mm triplets I've seen.

Is the 1000D a good camera to practice on, if the ultimate goal is a 6D? Shall I expect the same issues?

On 17/12/2016 at 16:08, Marf1 said:

I want debayer my sony nex 3...is it possible??

Heard about nex5, it should be doable. Grab a few spare sensors from ebay to stay on the safe side.

On 12/13/2016 at 21:31, zfedoran said:

Has anyone tried using liquid nitrogen to remove the sensor glass? 

Just ran across this video, it would be interesting to see if this or dry ice can be used to remove the protective glass over the sensor.

Wow, that's interesting . I need to grab a 1$ sensor for that test - however, that doesn't prove that a 6D sensor would survive the icing + thermal shock. Actually I could avoid icing by blowing argon on the sensor until it's room temp again, the question is just, if anything cracks in the sensor stack (electrodes, optical pad)?

Thanks for the great deal of info you are sharing us Brent. The existence of the "optical pad" is true, you can clearly see them on the chipworks electromicrograms.

Is it difficult to get the oak "singing scratch free"? If possible I am aiming to have a clean flat, that I can use the cam for normal daylight shots too.

Videos are very welcome! There is not much on youtube, a few monents of old, 350d-450d conversions, but nothing on the "real thing" how e.g. a mono 6d comes to this world:). Once I get there i will document every move at least with photos.