johninderby

Not a problem in the UK at least with my 5" refractor. Does seem to handle heat better than the Baader Cool Wedge I used to have. Did use the Badder with a 6" refractor and that did get very hot after a while. The Baader was fully enclosed and so didn't get rid of heat very well with the 6". The Lacerta with it's open bottom design has much better cooling so should handle the 6" OK.

            John

They also do a 1.25" version that's very well priced but they recoomend going for the 2" for scopes over 100mm.

           John

Underside of wedge.

Size comparison with 1.25" diagonal. 

It hasn't been out that long and not yet common in the UK but I think it will become popular once word gets around.. About half the price of the Baader too. Built like the proverbial tank. Check out the thickness of the metal housing. Lacerta seems to be an Austrian brand and quite popular in Austria and Germany.

          John

Lacerta Brewster-angle 2" Herschel Wedge - First Light

My new Herschel wedge arrived the other day and got it set-up with my Orion 120mm f/5 frac.

Impressed with the sheer quality of the wedge. Very, very solidly made and has the feel of a big hefty piece of industrial equipment. This wedge has a Brewster angle of 56.6 degress instead of the standard 90 degree angle. This allows for better polarization and gives a wider range of adjustment.

Although this design has an open bottom for better heat dissapation it's not to be confused with the old style Intes wedge that had an open bottom that let a potentialy dangerous beam of light shine out. This is a very dfferent design that doesn't allow any stray light to escape. You can actually look stright up into the open bottom of the wedge with no danger. See the two relevant pics.

The angle of the prism is also adjustable. Mine didn't need adjusting but it's nice to know I could adjust it f I needed to.

Manufacturers blurb:
"Most commercially available Herschel wedges (like INTES, Lunt, Scopium, Baader...) come in a 90-degree variant.
The Lacerta Herschel-wedge features a significant, 56.6-degree angle, so called Brewster-angle that provides a special benefit when compared with other 90-degree Herschel wedges.
This befenit is coming from the fact that nearly 100% of light is polarised under this angle; this means that the Lacerta Herschel wedge offers continuous or even complete dimming with the mandatory ND=3.0 filter and an additional (optional) polarising filter. In reality a dimming range between ND=4.07 and 6.37 or even more can be achieved.

Without the polarising filter the Herschel prism operates at ND 4.07 that is very good for photography. The 90° "traditional" Herschel prisms can achieve ND=4.24 to 5.00."

First Light:
Although there's nothing to be seen worth mentioning at the moment it did show good surface granulation and the image was nice and sharp. I used a Baader Solar Continuum filter and a single polarizing filer. Haven't tried the IR cut filter yet. I used to have a Baader Cool Wedge a while ago and initial impressions are the Lacerta seems to be every bit as good. Also have used a Lunt wedge and would have to say the Lacerta was a bit better.

Conclusions:
A worthy competitor to the Baader Cool Wedge and cheaper as well and has potential advantages over the Baader for photographic use. Does require a fair bit of infocus and I found with the Orion 120mm f/5 focus was just about achieved at full infocus travel with the zoom eyepiece I was using. I have trimmed 20mm off the OTA tube to allow for extra infocus travel which won't be a problem with usng the scope for other that white light solar as the new focuser has 20mm more travel than the stock one.

        John

The FT R&P focusers should not not need any major adjustment or lubricatrion and should last a lifetime. They simply never wear out. As it's second hand I would think it most likely that the scope has been dropped and the focuser damaged. Another possibility is that someone has taken it apart and not been able to put it back together again properly.

I think it will probably need returning to Starlight Instruments for repair.

John

When you compare the price of smaller MAKs and SCTs there is a big price difference as the MAKs can be made without the need for expensive handwork to finish them off.

John

That's excellent John. Thank you for posting it.

To summarise, assuming I've understood correctly, it pretty much means that "During assembly the corrector, primary and secondary are matched as a set if necessary by refiguring the secondary mirror and if the corrector is broken any replacement may well require the secondary altering to suit". Does that sound right?

James

That sums it up pretty well I think.

John

This quote from Bob Piekiel will explain quite a bit on the subject.

*************************************************************************************************************************************************************

The corrector isn't actually "matched to the scope. Rather, the corrector

is made to a pre-determined mathematical calculation and is not always "perfect"

when it comes off the assembly line, so the scope is usually "tweaked" to make

the system null when the final assembly is done.

Celestron does this by hand-figuring the secondary mirror to remove residual

aberrations in the system. Meade does it by "parts swapping" (trying different

primary/secondary/corrector combinations) until they get a system that nulls.

Celestron correctors are all usually a bit different than each other (Meade

tries to hold them to a more uniform level) so if you break one any try to

replace it with a surplus corrector or one from another scope, it usually makes

the scope give very poor images, which would need the secondary mirror

re-figured to correct.

If you send your scope to the manufacturer, they will replace the corrector and

re-match the system, for a hefty fee (usually a few hundred dollars, depending

on the size).

Even though the optics in both Celestron and Meade are "rotationally matched"

the optics themselves are made on automated polishing machines that spin them,

so they're figures of revolution and theoretically should be free of

astigmatism. Indeed, astigmatism is very hard to match out, compared to other

types of aberration (spherical, etc). Therefore if you have a scope with a

mis-rotated corrector, you can try star-testing it and rotating it in 90-degree

increments, seeing which position gives the best images. Fine-tune as you go,

but collimation and centering is going to be more important than rotational

orientation.

Correctors with simple radial cracks usually pose no degradation to performance

at all, and can be simply left alone.

The questions you are asking are big ones, and it is difficult to explain the

answers in a couple paragraphs. All of this info can be found in detail in my

two books "Celestron The Early Years" (ebook) and "Testing and Evaluating The

Optics of Schmidt-Cassegrain Telescopes." They both contain highly detailed

descriptions of how the optics are made, figured, and why they work the way they

do. They contain detailed interviews with Celestron opticians and matchers, as

well as inside tips and info found nowhere else. My SCT testing book has

chapters describing secondary matching procedures for the more ambitious ATM.

Together, they will make you an "expert" on the topics of your questions.

I've regularly talked about both books here many times. I advertise them on

Astromart, and have an ad running there now under the "Catadioptric" section.

Best, Bob Piekiel

*************************************************************************************************************************************************************

Well worth getting his books as well.

John

The correctors and primary mirrors do differ slightly when they come off the production line so Celestron matches them up to cancel out errors and then touches up the secondary to complete the job and produce a matched set.

John

Already had a spare B&W case so just got some new foam for it.

John

Did someone say X-Cel LXs in their own case.

Little package from FLO arrived this morning to finish off my X-Cel LX collection.

John

Or a Star Vacuum Cleaner

John

Yes the adaptor will fit onto the photo tripod which then allows any mount with an EQ5 type fitting (EQ5, Skytee 2 etc.) to fit. However with the Skytee 2 you will need a heavy duty photo tripod, at least a load capacity of 12kg. Should be OK with a small 127 OTA.

Please note though that while it will work OK it won't be quite as solid as a proper astro tripod.

John

The 200 is a nice size, enough aperture to give great views, but still "small" enough to manage easily.

I've always found Harrisons easy to deal with and very helpful. The man on the phone is indeed very knowledgeable. He was with Telescope House for many years, their loss and Harrisons gain.

John

Many thanks for the drawing, I think the adapter should do the trick

That's good.

BTW I ordered the adaptor directly from Berlebach. Only took a few days to arrive.

http://www.berlebach.de/?bereich=details&id=117&sprache=english

John

I was looking at the adapter to mount my Giro III on my Giotos 9730 photo tripod.

The Giro has the Vixen EQ5/HEQ5 fitting. Do you think, with the bit that has the M10 thread in it sticking out 2 cm it would fit the adapter?

Here's a rough sketch of the adaptor.

John

I was looking at the adapter to mount my Giro III on my Giotos 9730 photo tripod.

The Giro has the Vixen EQ5/HEQ5 fitting. Do you think, with the bit that has the M10 thread in it sticking out 2 cm it would fit the adapter?

I think it should fit but I'll check the dimensions of the adaptor and let you know tomorrow.

John

Another installment in the Skytee-2 saga

Although I am pleased with the Skytee 2 Alt-Az mount on an HEQ5 pillar I wanted to try it on a good heavy duty photo tripod for a more grab'n'go setup.

I already had a nice solid Manfrotto 475 tripod, but the only problem is that it has a 3/8" fitting and the Skytee 2 has an M10 connection. After looking around I found that Berlebach in Germany makes 3/8 to M10 adaptor that allows you to fit any standard astro mount such as an EQ5 or Skytee 2 to a photo tripod. You simply screw the adaptor onto the bottom of the Skytee 2 mount and then screw it down onto the tripod.

I've tested it with my solar observing setup (Lunt60 Ha & TS80/480APO) and it's really solid with virtually instantaneous settle down times if you tap one f the scopes.

I've also briefly tested it with a 6" f/8 newt and the TS80 APO and it's still good, although vibration settle down times are a few seconds. While the vibrations are settling down they are a slow speed oscillation that doesn't really interfere too much with observing.

So overall the combination of the Skytee 2 and Manfrotto 475 tripod really works. The solar setup can easily be carried outside fully set-up and ready to go so it meets my definition of grab'n'go. Or of course it would easily handle a 4" or 5" refractor and still be grab'n'go.

John

Oh my John, I think I may have just wept inside a little. What scope/s do you use with those?

They're used with my FLT98 FT, TS 80/480 Triplet, 150PL Newt (OO 1/12PV mirror), OO 14" dob (1/11PV mirror & StellarCAT) and the zoom with my Lunt 60ha.

John

That 3.7mm Ethos looks massive! Only five main eyepieces in that cast too and yet so many magnifications and exit pupils are catered for. Well thought out.

Ant

Yes that 3.7 is a bit of a beast isn't it

Just for interest I've weighed the eyepieces.

• Televue 3.7mm SX Ethos - 590 g.
  
• Televue 6mm Ethos - 440 g.
  
• Televue 13nn Ethos - 565 g.
  
• Televue 35mm Panoptic - 720 g.
  
• Penatx XF 6.5-19mm Zoom - 240 g.
  
• 1.5x APO (Japanese) Barlow element - 28 g.
  

John

My Eyepiece Case (latest)

The contents of my eyepiece case have been changed around a bit since getting the 3.7 SX Ethos but here's what's in it now.

• Televue 3.7mm SX Ethos
  
• Televue 6mm Ethos
  
• Televue 13nn Ethos
  
• Televue 35mm Panoptic
  
• Penatx XF 6.5-19mm Zoom
  
• 1.5x APO (Japanese) Barlow element
  

With the 1.5x Barlow element this gives me a 2.46mm, 3.7mm, 4.0mm, 8.6mm and 13mm Ethos line-up, although really the Barlow is only used with the 13mm to give 8.6mm. The Barlow element is the one that comes with the A&E Supreme Barlow and it's a Japanese made triplet APO that works extremely well, although at around £88.00 it's not cheap for a 1.25" Barlow. The Pentax zoom is a nice lightweight and compact zoom and is primarily used for solar viewing although it also performs well in regular night-time use.

All in all this gives me whatever mag I want in just one compact eyepiece case.

John

The Pyrex does cool down faster than plate glass. While it's true to say that there's no performance difference when they're both cooled down there is one very important additional factor to take into consideration. If the temperature is falling the Pyrex tracks the temperature change better than plate glass.

The bigger the mirror the bigger the problem with cooldown, which is why premium scopes with big mirrors use low expansion glass.

John

Now let me see........ They're both low cost entry level Ha scopes and the Lunt 35 and PST are about tied in overall performance, despite the PST having 14% more aperture, and the Lunt costs less than the PST. The biggest headache with the PST is that dammed small "sweet spot" which means that you can only see a small part of the surface in any detail at any one time. That's the reason I got rid of my PST.

John

If you get the Skywatcher Maksutov to SCT adapter http://www.firstlightoptics.com/proddetail.php?prod=synta_SCT_adapter then you could fit any SCT type Crayford focuser.

John