Deadlake

I believe the 140 mm has got a poly-Strehl around 0.92, so how many nights of the year will you be able to make use of a scope with a higher Strehl? 

Note, TMB defined 0.95 Strehl as a limit where a scope would be seeing limited most nights of the year, so why engineer more?

I’m sure your SXD2 would be able to handle the 140 mm, so unless portability is a requirement I’d go with the larger aperture.

Also how much overlap with you Mewlon 180?

Always good to have a 4” for flexibility, does it need to be a DZ?

On 23/04/2021 at 10:23, GavStar said:

It was good to be able to do a meet up after such a long time. Shame I forgot that I didn’t have a diagonal attached to my AP130GTX! However luckily I had my tec turret to use instead which was quite fun to rotate around for easy magnification changes.

 

Surprised no NV intensifier attached. 😄

On 29/05/2021 at 18:00, globular said:

I have the Baader 2" Prism diagonal and like it very much.

It does indeed have a mechanical light path of 100mm which is 12mm less than the Baader 2" Mirror at 112mm - however light passing through the prism (rather than reflecting off a mirror) does use up some of the back focus; but only a very small amount.  I'd reckon you'd save around 10mm over the mirror diagonal.

Have you considered the Baader 2"/90° Astro Amici-Prism with BBHS coating?
https://www.firstlightoptics.com/diagonals/baader-290-astro-amici-prism-with-bbhs-coating.html
This has a light path of 85mm - so you'd get another 15mm over the 2" Prism and 25mm or so over the 2" mirror.
Not sure how compromised the view is though, in order to achieve the erect image; and it is quite a bit more expensive.
All depends how much focus travel you need to achieve.

You're right to stick with 2" though - a T2 diagonal does have a shorter light path but does not have enough clear aperture (33mm) for your 30mm UFF (38mm).

It’s a good idea, the Amici is not listed here in comparison with the other available 2” diagonals:

https://www.cloudynights.com/articles/cat/articles/mirror-vs-dielectric-vs-prism-diagonal-comparison-r2877

Not sure if this is enough infocus.

As discussed Stu, several sites 30 minutes from Walton Green that are > SQM 20.69. When I arrived home after the meet-up a couple of weeks ago you could tell the difference in sky brightness. I was tempted to keep on viewing but school night.

"..the one I’m not supposed to mention by name..."
 

I thought you took the dob 😃

On 29/05/2021 at 19:01, John said:

This is still my situation so I can't help on the 2 inch versions.

Still using my 1.25 inch eyepiece set with the Tak - I do think that they suit the F/9 scope well and the 24mm Panoptic gives a 1.81 degree true field which fits most things in.

I have other options if I want to go wider .....

 

 

Did the moonlite focuser you outfitted your Vixen with reduce the optical path length? 

Another valid approach?

Revising this thread. I have a APM XWA 17, 20 mm and 30 mm UFF EP’s. I find using a Baader 2” dialectic not enough in-focus available to gain focus. I note that the Baader 2” dialectic and BBHS mirror diagonals have an optical path length of 115 mm whereas the 2” prism has an optical path length of 100 mm. I’m hoping the 15 mm decrease in path length of the prism diagonal will be enough to gain focus with the XWA and UFF EP’s. 

Does anyone have any experience of this?

1 minute ago, Stardaze said:

Definitely. As a very keen photographer, who has suffered from owning far too many bags (down to 4 currently), understand that bags are very personal things. At £20, it looked a no-brainer. Incidentally, I'm not personally keen on the ruck sack style, purely down to the access of them, but they certainly work for many. 

Can be bought separately from a flight case:

https://www.vanguardworld.co.uk/products/supreme-46d

Just now, Kon said:

That's a nice padded bag; where did you get it from?

It's one of these:

https://www.vanguardworld.co.uk/products/divider-bag-46

Sold on amazon or most camera shops, around £70.

A camera bag is very flexible and at night easy to find which EP, filter you are looking for.

This bag also fits it side a hard flight case.

@GavStar Has written a good comparison between OVNI and PVS-14 based intensifiers which will save you having to wade through the CN threads on the subject.

While the OVNI does have the cherry picked harder tubes and the prime feature, I think its up to OVNI to respond with a better lens

• Matches the PVS-14 Envis lens
• A little more adaptable on the filter front.

Jonathan @OVNI does know this limitation and has responded on CN he intends to offer an Envis type lens if/when he can source one.  

Well done Gavin and PeterW

37 minutes ago, John said:

Or start to quibble about the spec as they do on another forum that I can think of !

 

 

You mean where someone get a better number and they send the scope back? Which forum could that be on. 😁

However as you know from another thread on this forum, you can publish RMS, PV and Strehl and those scopes are still third division due to Abbe number for the glass. 😉

6 minutes ago, John said:

Yes - I was surprised, but pleased, to find this spec in the public domain when I bought my LZOS refractor.

 

If people have to much information they can make an informed choice....

Manufactures publish Strehl, where is the PV measurement??? 

20 hours ago, Stephenstargazer said:

Maybe but Berlebach heads are neither cheap or quick change. You can also buy a tripod with an EQ5 head to use with the Rowan adaptor, and get a little 45mm insert Berlebach make to suit Vixen SP etc. 

I think the choice depends on how you intend to use each of these mounts. Good luck!

Looking into the vixen route, its quite a lot of buy the 45-60mm adapter( part #75169) and then the Rowan M10 adapter. I agree the stability will take a hit over a purpose built solution.

Back to the T-Pod, this works as reported on CN. You need a NEQ6 adapter here, https://www.avalon-instruments.com/products-menu/accessories/eq6-tpod-mounts-adapter-kit-detail

This should also work the Geoptik Hercules tripod, which is cheaper than the planet but with some limitation around height adjustment.

The stability of the Planet/Hercules and T-pod is the same so you are down to cost and weight and lets be honest of the below the Planet and The T-pod look the best.
 

Hercules

Around £400  + NEQ6 Adapter is £30  + case £65 = £495 weight -> 10 kg

Planet

£599 + case £89 = £688 weight -> 11 kg 

T-Pod 110

£769 + NEQ6 adapter £30 (case included) = £799 -> weight 6.9 kg

For the T-Pod you are paying £100 for 4 kg weight reduction and also cheaper adapters then the Planet.

However the Hercules is a great value option.

2 minutes ago, Stephenstargazer said:

No! The SXG HAL is for Sphynx etc mounts with 45mm spigot. The part to convert this to 60mm is #75169.

I tried my HAL tripod with the Rowan and it is marginal. OK with single 100mm refractor but that is a fraction of mount capacity. It is though a lovely light tripod for transport, if you have one already. With 2 adaptors, Rowan and Vixen, it is not economic.

( I also have a Vixen fit pier so the adaptors are useful for that to me)

The path of least resistance is to buy the Berlebach and then purchase a separate head for the AZ100 and then Vixen mount. 

36 minutes ago, Stephenstargazer said:

Yes but the HAL tripod can be adapted to a 60mm recess with a Vixen part.

The SXG-HAL130 has a 60 mm recess?

This adapter converts to he SGX to a 45 mm recess to be used with older vixen mounts.

https://global.vixen.co.jp/en/product/25169_8/
 

If the AZ100 needs a 60 mm recess I should be ok?

1 minute ago, DesertSky said:

Dear Proto Star,

This is not data but a flood. This is a  typical pattern of internet trolls. You have disclosed yourself and your sponsor, I think.

I have access to the data because I got to choose a lens cell.

Also vendors cannot refute claims posted on this forum. Maybe @Stu that should change?

I think you have not changed your dogma when supplied with the data, I don’t see any scientific approach in your reasoning.

1 hour ago, Stephenstargazer said:

the newer Vixen tripods are 45mm  recess so not ideal.

You mean like the HAL tripod, the bolt is not long enough?

Has anyone used a t-pod here with the AZ-100?

11 hours ago, Stephenstargazer said:

But it's not even made of wood! 😁

Who cares in the dark when you are putting it all back in the car? 😃

There is a cheaper model here

https://astrograph.net/epages/www_astrograph_net.sf/en_GB/?ObjectPath=/Shops/www_astrograph_net/Products/AGSMCYG42
 

but a 3/8 bolt.

has 2 M8 holes as well.

29 minutes ago, DesertSky said:

I honestly believe that I will not be able to differentiate the visual qualities of the glasses FPL51, LZOS (FPL 52 similar) and FPL53 (or FCD100) because I am only a visual hobbyist and not imaging deep sky.

On the other hand, I have a strong scientific educational background and  I work hard for the money. That helps me to judge the fair market value for a product. I would not pay a price of gold for the silver. LZOS is a marketing phenomenon. If there is someone claiming that LZOS is a TAK, TEC or AP similar product, I want to see the data. not only words.

If you strong scientific background then look at the below numbers for 130mm/F6 lens produced by LZOS.

The main point is that the performance of a lens is theoretically until its has been placed on an optical bench and the results measured. Looking at ABBE numbers does not give you enough data.

The cost of figuring is very prohibitive. Moving all of the below lens to a Strehl >= 0.98 would require a rise in cost of the lens cell by 25% (that was the charge for the LZOS anniversary addition).

My choice of LZOS over AP was not cost but waiting 10 years.

Glad I bought when I did as LZOS current production run is bought until January 2023.

Note: The below a list of 44pc 130/6 lenses from the last two years, 2019-2020.

 S/N.             RMS.         PV         Strehl

8 hours ago, Stu said:

Isn’t that quite a short list? 😉

Your quite right, there are so many observation list already available, even the sharpless catalog. And you can share lists as well. Great feature.

I know the AZ-100 can be mounted on a T-Pod tripod, but has anyone used a carbon fibre based tripod at all? Trying to reduce weight for dark site or club meet ups and the AZ-100 is heavy enough (but lighter and less faff then a GEM). 
 

I was thinking of a:

https://global.vixen.co.jp/en/product/25164_3/
 

with a m10 pier puck.

3 hours ago, Stu said:

I never use any astronomy apps in that way (pointing them at the sky and expecting to be told what’s there) so it’s simply not an issue. I don’t apologise for ‘bigging up’ SkySafari, it’s an excellent app and drives a lot of my pleasure in astronomy, along with this forum.

Indeed so many stars which one am I looking at. However for planning, and then getting the mount to slewing through a list of double doubles or seeing what’s up tonight amazing.

I’ve been using an unreleased version of Luminosity which has better rendering then sky safari, unfortunately no way to share viewing lists like the Pensack 500. However can drive a starbook mount.

On 14/05/2021 at 11:53, chrispj said:

It's around 20.8 according to lightpollutionmap.info. If I pop up to the common behind the town I could apparently get to around 21.2.

@Stu some pages back. 
 

The other question I would ask is what kind of mount does @chrispj want to use?

For DSO’s I like to have goto (some of us don’t live under 21 SQM skies) and this helps a lot. In that case I would be tempted by a C9.25 and Mewlon, however apart from the design characteristics that @jetstream noted they also have mirror flop, which I know some people could not live with and sold them. Have spoken to people who have had both the Mewlon and C9.25, it’s make the jump to the 250 as no mirror flop and the built in fans work well and the smoother Tak mirrors give more contrast then the Celestrons for DSO work.

The other option would be 10” GSO Cassegrain, which have no mirror flop and cool quickly. The main issue is the weight. ATS uses the mirrors in there scope, I’ve attached the reflectivity report:

DatenblattCZ303-01 - Normal.pdf

GSO makes a research grade mirror as well,  but that needs to be parked up the top of a dry mountain otherwise the surface degrades in a year:

DatenblattCZ322-01 - Enhanced.pdf
 

In both cases I’d need to change my observing habits and the scope out hours before viewing with their built in fans running.

Obviously all depends on temperature gradient and time of year to how quickly if a reflector based scope acclimates in ever during the night.

34 minutes ago, Stu said:

I say this without wanting to stir up a load more trouble, but it actually happened....

Last night, I was observing with my local group, and one chap turned up without his scope. At one point I offered him a look at the Moon through my Tak FC100DC, which he accepted.

His words were ‘Wow, that’s better than my 10” dob”.

Now, I know from experience that my 8” f8 will show better detail at high power due to its resolution so I’m not going to argue that. I guess it’s a case that at the x148 I was using, the Tak gives a very nice, clean and contrasts view which is very appealing.

I shall now don my tin hat and seek refuge under the table 🤣🤣

#justsayin’

I was actually there. Seeing was quite good, better then expected. My ears did pick up as the above word where uttered. The cogs in my brain where turning about posting on this thread. 😀
One thing I would say and it’s the first time I went mobile was the flexibility of having a 4” refractor to setup, use and take down. 

Thanks @Stu for organising, shame @GavStarwas missing in action. 😀

19 minutes ago, niallk said:

I keep a 15" dob ... assembled ... in our bedroom! 😂

That’s a great photo, always good to put things in perspective 😃👍