Telrad Riser

[Andy ES]

Hi

I'm thinking of getting a telrad finder as I’m struggling a bit with the 8 x 50 finder that came with my 9.25 SCT.

can anyone advise please if it’s worth getting the riser for it either 2 or 4 inch?

also is it best to install it at the eyepiece or corrector end.

Thanks for any advice or experiences.

 

[johninderby]

On a newt or dob yes it’s very useful. on an SCT etc not really needed.

I tried the 4” on my dob and found it just too high. Find the 2” is just right.

Edited January 26, 2021 by johninderby

[AlexK]

You forgot to clearly state your instrument and mount models (you can add its description to your forum signature, see mine below? Or if you don't know at least make a photo of it and attach to the post). Without that it's hard to judge which (or if) Telrad riser would be more beneficial in your situation and most of advice will be just guessing.

In general, however, the riser or not depends on your pointing and observing flow. So in fact in addition to the above you need to answer the following as well:

1. Are you using the EP diagonal?
2. How you are pointing your SCT to invisible objects (e.g. Galaxies)?
3. Are you sitting or standing when pointing?
4. What about when observing?
5. How you are storing your SCT when done observing?

Depending on your answers certain recommendations might be irrelevant.

Edited January 27, 2021 by AlexK

[Andy ES]

OK thanks here’s some extra info to asses:

Celestron CPC 9.25 Alt Az dual fork mount the centre of the eyepiece of the current finder stands off the tube by 50mm (2”)

using 2” diagonal

most pointing done by computer

standing while pointing & observing

Scope stored striped down of accessories in garage.

Telrad mostly going to be used to assist with 3 star alignment process. I’m finding it fairly difficult to locate stars initially in the finder.

Thanks again hopefully someone has used this set up.

[Spile]

I note that some have mounted the Telrad actually on the finder which does away with the need for a riser but after considering it, I decided to place it on the OTA to the right of the finder bracket.

[AlexK]

15 hours ago, Andy ES said:

OK thanks here’s some extra info to asses:

Thank you for the details.

So, it looks like you are observing bending forward, like looking into the microscope. Thus the mount is sitting rather low. In that case even for a 10"+ SCT OTA it is most convenient to have a tallest riser you could get, so you can transition from the EP view to the straight-through pointer simply rising your head up. That would also provide a better background view to look for your target star unobstructed with the OTA and the fork.  I would install it centered on the farther end of the OTA to avoid bumping into it when observing and to allow pointing close to Zenith as the long stalk will overhang the base enough to get the view under it.

Also, as you are not likely planning on learning any advanced Telrad pointing techniques like the TPM (having the GoTo), going to have it far from your eyes (parallax issue is negligent), and don't really need it anywhere after the star alignment (dark adaptation is not there yet to care about) you can save the weight, bulk, and the take-down time (possibly some dough as well) by opting for a simple RDF instead of the Telrad. I would recommend cheap reflex gun sights like this one:

Large window, adjustable brightness, Alt/Az reticle option, easy to wipe dew. The price is on par with Telrad though (I bought mine on eBay a long while ago for just $5). There are risers for the picatinny rail as well. And most are far cheaper than astronomy risers. Just look in Airsoft guns "section", not in real guns

To make sighting on the far end of the OTA easier, I'd recommend placing a sticker on the near side marking the position to line up the eye with the RDF mirror ring so you could find the dot in the mirror easier. You can put it closer to amend the latter, but these sights have some parallax (especially if your own eyesight is not 20/20), so too close sighting might reveal it.

Edited January 28, 2021 by AlexK

[Andy ES]

Alex

Thanks very much for you time and trouble in answering these questions, really appreciate your advice.

regards

Andy

[Andy ES]

Got and been using the 2” riser which works like dream and is also the most expensive bit of plastic I will ever buy! 😬

[AlexK]

Congrats!
Yeah, the demand is on the rise, so as the capitalistic opportunism these days...
That's why I've got a decent 3D printer 7 years ago. Saved tons of money on all these simple essentials (for "homesteading", astronomy, and other hobbies) already.
By the way, the most advanced collimating pointer of 21st century, the QuInsight, is also fully 3D printed (surely except for optics and electronics) and also with the "integrated" 5" riser  (you don't need it, it's for the TPM-like flow without a GoTo).

[Andy ES]

I couldn’t believe how much easier and quicker the alignments are to do now.

Don't know why Celestron don’t ditch the finder and put one of these on their goto scopes or put the savings into supplying  a decent diagonal. Old habits and traditions I suppose.

[AlexK]

7 hours ago, Andy ES said:

Don't know why Celestron don’t ditch the finder and put one of these on their goto scopes or put the savings into supplying  a decent diagonal. Old habits and traditions I suppose.

Nah. An optical finder is perceived by buyers as an additional mini telescope bonus with obvious and legit use case. While the RDF as an inferior to it pointer, and Diagonal is like a very optional accessory. While that's all not true, every little lie creates a better margin  

[Stu]

@AlexK am I right in saying that what you describe as TPM is simply using a Telrad type device as it was intended? Ultimately it’s as simple as matching the Telrad circles with a referenced set of circles on an app (SkySafari in my case) and aligning the visible stars correctly so the target is centred. Not sure it needs to be much more complicated than that?

The QuInsight device looks interesting. Is this something you are involved with commercially? Having the wider field of view seems very useful vs a Telrad. Is there a way of preventing seeing as it seems quite vulnerable to this.

Thanks 👍

[AlexK]

Hi Stu.
Yes, you are 100% correct about the TPM method. It's just that simple, and that's how Telrad was initially perceived. But back then it was quite an elaborate mental procedure as paper charts could not follow the real thing orientation, so you could not use Telrad rings gaps for direct matching (see below). The complications though are created by apps developers. Last time I was checking, the SkySafri had a very dumb Telrad reticle implementation with permanently fixed sizes of the circles and its gaps orientaton. The 1:1 (photographic) reticle representation on the chart is a bit doubtful to me as well. So if you actually try comparing your chart's screen view with the view in Telrad side by side, you will see that you cannot match the two exactly (in my writeup I have outlined all possible reasons for that).

Such a primitive implementation could still be leveraged. Just get used to making little mental adjustments here and there when matching patterns (the centrality over the stars pattern is the key). But the accuracy will be significantly less stellar esp. for a beginner. The TPM's point is to utilize your inborn ability to perfectly match the stuff you see with the mental model. The human mind is quite bendable with practice though :))))

Also I know folks utilizing app's (SS and several other apps allowing that) eyepieces circles to amend that problem: just create 3 fake custom eyepieces and play with their AFOV parameter until the corresponding circles on the chart are matching the outer edge (or inner, just make sure it's a consistent edge to remember which) of the Telrad pattern you see in the sky. The single time effort worth doubling your TPM accuracy permanently. But with that you usually can't use Telrad gaps for matching still. There could be a way out as well: check if your app can show any crosshairs in the circles. If you are on an Alt/Az mount you want it to show Alt/Az crosshairs, on an EQ mount you want meridians/parallels-matching crosshairs displayed. Then you have to mount your Telrad on the scope so its gaps are matching the crosshairs lines. Usable with some inconveniences, but that's also the intended Telrad use way (gaps where supposed to show where the view moves as you push/pull the telescope on the mount in one axis, same purpose as those EPs crosshairs). Lately a well forgotten feature, as the viewing convenience is more appealing to folks using it as a trivial RDF :))) Though, if you at least pay attention to these gaps when moving the OTA, they are of a tremendous help when fighting the "Dobsonian hole" (problem pointing with the Dob near the Zenith).

The above method, by the way, would allow to add all wider QuInsight circles to the existing Telrad ones in a pinch (by the way, the QuInsight reticle is also independently rotatable by the side screw head).
DSO Planner is not affiliated with the Rob's creation (QuInsight manufacturer) in any way, but I'm a really happy buyer! And I've been in tight contact with him directly when being ordering mine, as I needed a special manufacturing order for the glass mirror (better transparency) and a particular base box lid alterations (to incorporate my blinker circuit in it). Sure thing, I have implemented the native support for QuInsight in my app as soon as I got my hands on it and realized that's the true game changer for the TPM use cases expansion! Still highly recommend it!

Umm, not sure what you mean by: "Is there a way of preventing seeing as it seems quite vulnerable to this" ?? Please, elaborate.

Edited May 6, 2021 by AlexK

[Stu]

16 minutes ago, AlexK said:

Hi Stu.
Yes, you are 100% correct about the TPM method. It's just that simple, and that's how Telrad was initially perceived. But back then it was quite an elaborate mental procedure as paper charts could not follow the real thing orientation, so you could not use Telrad rings gaps for direct matching (see below). The complications though are created by apps developers. Last time I was checking, the SkySafri had a very dumb Telrad reticle implementation with permanently fixed sizes of the circles and its gaps orientaton. The 1:1 (photographic) reticle representation on the chart is a bit doubtful to me as well. So if you actually try comparing your chart's screen view with the view in Telrad side by side, you will see that you cannot match the two exactly (in my writeup I have outlined all possible reasons for that).

Such a primitive implementation could still be leveraged. Just get used to making little mental adjustments here and there when matching patterns (the centrality over the stars pattern is the key). But the accuracy will be significantly less stellar esp. for a beginner. The TPM's point is to utilize your inborn ability to perfectly match the stuff you see with the mental model. The human mind is quite bendable with practice though :))))

Also I know folks utilizing app's (SS and several other apps allowing that) eyepieces circles to amend that problem: just create 3 fake custom eyepieces and play with their AFOV parameter until the corresponding circles on the chart are matching the outer edge (or inner, just make sure it's a consistent edge to remember which) of the Telrad pattern you see in the sky. The single time effort worth doubling your TPM accuracy permanently. But with that you usually can't use Telrad gaps for matching still. There could be a way out as well: check if your app can show any crosshairs in the circles. If you are on an Alt/Az mount you want it to show Alt/Az crosshairs, on an EQ mount you want meridians/parallels-matching crosshairs displayed. Then you have to mount your Telrad on the scope so its gaps are matching the crosshairs lines. Usable with some inconveniences, but that's also the intended Telrad use way (gaps where supposed to show where the view moves as you push/pull the telescope on the mount in one axis, same purpose as those EPs crosshairs). Lately a well forgotten feature, as the viewing convenience is more appealing to folks using it as a trivial RDF :))) Though, if you at least pay attention to these gaps when moving the OTA, they are of a tremendous help when fighting the "Dobsonian hole" (problem pointing with the Dob near the Zenith).

The above method, by the way, would allow to add all wider QuInsight circles to the existing Telrad ones in a pinch (by the way, the QuInsight reticle is also independently rotatable by the side screw head).
DSO Planner is not affiliated with the Rob's creation (QuInsight manufacturer) in any way, but I'm a really happy buyer! And I've been in tight contact with him directly when being ordering mine, as I needed a special manufacturing order for the glass mirror (better transparency) and a particular base box lid alterations (to incorporate my blinker circuit in it). Sure thing, I have implemented the native support for QuInsight in my app as soon as I got my hands on it and realized that's the true game changer for the TPM use cases expansion! Still highly recommend it!

Thanks Alex, all interesting stuff.

I actually often use my Telrad in the RDF manner to get me on to a known star, then do my star hopping using SkySafari with a field of view circle set to match that of my eyepiece. I then just match star fields, hopping across in the general direction of my target until I get there. That is all probably because most of the time I observe from pretty poor skies, so even spotting a star as a start point with a Telrad is an achievement! 🤪🤪. Under darker skies, the Telrad used properly is a very handy tool I agree. Next time I’m somewhere dark,  I’ll check out any difference between actual and simulated Telrad circles on SkySafari and see what I find.

Cheers.

[AlexK]

I understand the city dwellers problem with that. The QuInsight might address that very well for you. 
I consider myself lucky as even at home, practically in between of the two whitest blobs on the LP map (San Francisco and Oakland) I have quite a usable sky darkness for Telrad after sitting under the head cover for ~20 min. 

Telrad is great at direct pointing as well, but a Zeiss lab microscope is amazing at pounding nails into wood too! :))))

By the way, I just mentioned above (when you been replying I guess) that I didn't understand you last question: "Is there a way of preventing seeing as it seems quite vulnerable to this". Let me know if I've answered it above already

Edited May 6, 2021 by AlexK

[Stu]

4 minutes ago, AlexK said:

By the way, I just mentioned above (when you been replying I guess) that I didn't understand you last question: "Is there a way of preventing seeing as it seems quite vulnerable to this". Let me know if I've answered it above already

Ah, that was a typo, thanks to autocorrect! Seeing should have said dewing....

[AlexK]

32 minutes ago, Stu said:

Ah, that was a typo, thanks to autocorrect! Seeing should have said dewing....

Gotcha. QuInsight glass is indeed slightly larger than Telrad's window to accommodate the wider AFOV. That might be making it more prone to dewing. However, Telrad dewing problem is quite overrated in my opinion. Lately, I'm just carrying a microfiber cloth (coming with nearly all glasses from China) in my dedicated astro-vest clean pocket, and when I see the glass getting foggy, simply wiping it on the spot. So far so good. The collimator don't need any wiping even when foggy a bit, as the reticle is still clearly visible.

Though, I saw that later models of QuInsight come with the flip-off lid over the top of the mirror, which is another easy way to prevent dewing for much longer simply flipping it back when done pointing. Also, I can see all the DIY measures used for Telrad dew prevention easily adapted for the QuInsight nearly as is. And there is a potential for more ways. E.g. I had an idea of placing the heater element on the inside of the QuInsight column and providing small air vents around the lens, so the heated air would escape it with the natural "chimney effect" draw and heat the collimator and the mirror naturally. Should convey it to Rob one day.

Edited May 6, 2021 by AlexK