New starter - after help deciding between Takahashi FC-76DCU & FC-100DC

[Surfer Chris]

It's been a few weeks since I last posted about the intended purchase.

I have been extremely busy with work over the last couple of weeks. Plus I was really struggling to come to a decision over the 76DCU or 100DC, so as a result the scope I ordered stayed boxed up for a few weeks!!! After the discussions on here I thought I was going for the 100DC, then a week later my mind switched back to the 76DCU and I had discussed with the supplier the possibility of returning and swapping the scope for the cheaper option. But shortly after that, a lot of potential work came in, and at the last minute I decided to stick with the 100DC....

[Surfer Chris]

Took it out last night and WOW.

Looked at Orion nebula, double cluster in Hercules, Pleiades, Andromeda (M31) & Mars with the kids. I think I was most impressed (blown away) with the star clusters & the Orion nebula. It was great to have the kids out and very excited about looking through the scope. My son seemed to really like being able to see M31 knowing it is 2.5 million light years away - even though it only appeared as a fuzzy flattened patch.

I have to admit though, I was a little disappointed with Mars. I could see a bright pinkish clear disc shape with a 5mm BST (seeing an actual proper disc was a first for me so that was great), but it was quite small. I think I could possibly make out some albedo markings in the centre of the disc. But I understand Mars has moved quite far away already since opposition? I also noticed that I could detect an ever so slight red and blue fringe either side of the disc? I wasn't expecting to see this? It didn't really bother me as such, and it really was minimal, but just left me wondering whether this is something normal? I have read that these scopes are essentially almost colour free? Perhaps it is something more to do with the cheap BST EP I was using?

I was also pleased to find that the objective didn't dew up quickly like I thought it might. I was probably out for 45 mins...and the objective stayed nice and clear. Before bringing the OTA back inside, I slipped it back inside the plastic bag it was shipped in, and draped a soft blanket over it to prevent moisture condensing on the surfaces and to let it warm back up slowly. Left the cap off overnight for everything to properly dry out in case any condensation did occur. My wife thinks I have gone crazy cradling the scope like a new baby! I am hoping to get a case sorted as soon as possible - to keep it safe as I carry it out.

In terms of eyepieces, I have purchased only three so far. A Baader Mk IV 8-24 zoom, the 5mm BST Starguider, and I thought I would try a cheap 10mm Plossl (the Plossl is so cheap at around £20 that I thought I would just see what they are like). I thought the Baader zoom might be useful for me to get a feel for what magnifications I want before choosing decent fixed focal lengths EP's. Plus I thought the Baader Zoom might be quite good for lunar observation - which I see myself doing a lot of. 

I haven't tried the Plossl yet - but I am not sure I will get on with that style of EP - the eye relief seems very short. The BST seems pretty good though in terms of comfort.

I tried adjusting the focus in and out whilst looking at a few bright stars. I had perfect concentric rings either side of focus. So hopefully that is a good sign?

[Surfer Chris]

Sorry - double cluster in Perseus in last post!

[John]

I'm glad you are enjoying the FC100 - sounds like it is already doing the business for you !

Mars is much, much smaller now than it was at opposition - it's whizzing away from us and the small pink disk with faint albedo markings is what will will have to put up with now until the next opposition in December 2022.

The red / blue tints you saw around the limb of Mars were most likely caused by atmospheric dispersion as Mars is quite close to the horizon mid-evening now.

 

Edited March 7, 2021 by John

[Surfer Chris]

Thanks John. 

I need to expand on the eyepiece collection. I was going to treat myself to perhaps one good new eyepiece on this current spending spree. Then perhaps look out for some good used EP's over the next few months.

So was thinking of ordering the 24mm Panoptic. I am guessing that this will offer a far superior experience (with wider FOV) compared to the 24mm setting on the Baader zoom I purchased. And I am not simply wasting my money buying an EP with a focal length already covered with the Baader zoom?

[Ricochet]

Buying a 24mm Panoptic is definitely not a waste. At the high focal length part of the zoom range the field is very narrow and so a wide field 24mm is more a necessity rather than an extravagance. The panoptic is an excellent eyepiece, possibly the best option for maximising the field from a 1.25" eyepiece. 

[John]

2 hours ago, Surfer Chris said:

Thanks John. 

I need to expand on the eyepiece collection. I was going to treat myself to perhaps one good new eyepiece on this current spending spree. Then perhaps look out for some good used EP's over the next few months.

So was thinking of ordering the 24mm Panoptic. I am guessing that this will offer a far superior experience (with wider FOV) compared to the 24mm setting on the Baader zoom I purchased. And I am not simply wasting my money buying an EP with a focal length already covered with the Baader zoom?

The Panoptic 24 is very nice. So is the Explore Scientific 24mm 68 and it's a lot less expensive.

The performance differences between today's eyepieces are not that huge to be honest with you. Thats not to say that there are no differences but they can often be quite subtle.

Just because an eyepiece costs 4x or more as much as another does not give you 4x more performance I'm afraid. An additional 10-15% more is perhaps more realistic !

 

[KP82]

2 hours ago, John said:

The Panoptic 24 is very nice. So is the Explore Scientific 24mm 68 and it's a lot less expensive.

The performance differences between today's eyepieces are not that huge to be honest with you. Thats not to say that there are no differences but they can often be quite subtle.

Just because an eyepiece costs 4x or more as much as another does not give you 4x more performance I'm afraid. An additional 10-15% more is perhaps more realistic !

 

Agreed.

For a f/7.4 scope the user will be hard pressed to find any differences in performance between the ES68 24mm and Pan24.

[Surfer Chris]

Hi Everybody.

Just wondering if I could ask for your opinions on a high power eyepiece selection for the FC100-DC? I know I said I would build up my eyepiece collection slowly over time....but I cant wait! 

Following on from the last post, I purchased the TV 24mm Panoptic in the end. So for eyepieces, I now have a 24mm Pan, 5mm BST Starguider, 8-24mm Baader Zoom, & a cheap 10mm Plossl. I now want to start getting a couple of decent high power eyepieces.

I have been getting on fine with the Baader zoom and the 5mm BST and enjoying lunar viewing with these, but feel like I want to push the magnification a little further than possible with the 5mm. I find the BST to be generally quite comfortable, and the eye relief good. With the Plosssl (the eye relief is about 10mm), although the views are crisp enough, I find that a bit close for comfort and also noticed the other day that it kept fogging up which was annoying. So I am thinking that something with a little more eye relief is better for me, and hopefully extra eye relief will minimise the fogging issue.

After a bit of reading up, I was thinking between a 4mm TV Delite and 4mm TOE. But think I have ruled out the TOE because of the eye relief.

So, if I go for a TV Delite, the next question (which I am hoping some of you guys might be able to help me with) is whether I should go straight in for a 4mm, or whether I should go for something like a 7mm Delite and 2x Barlow?

Speaking to a particular retailer yesterday, they actually suggested going for a 7mm or 9mm Delite and barlow rather than a fixed length 4mm EP. I think their reasoning was that I would generally get more use out of a 7mm eyepiece, and a 4mm alone would get limited use. But the person I spoke to also suggested that for higher power use, I might actually get a better viewing experience with the 7mm & 2x Barlow rather than a fixed 4mm EP alone? Their Barlow suggestion was a 2x Celestron X-Cel, or a TV 2x Barlow. I kind of thought that the extra glass presented by the Barlow would detract from the views?

Anyway, I am just wondering if using a Barlow would be problematic with the FC100-DC and the Tak prism diagonal that I have since I know these scopes have limited focus travel? If I was to purchase a 7mm Delite and a 2x TV Barlow (mounted into the Tak diagonal), would I still be able to achieve focus OK? I don't want to be having to unscrew any of the the Tak extension rings in and out to just use a Barlow. If I have to do that, I would rather just get extra fixed focal length EP's (i.e. get a 4mm Delite and a 7mm Delite and not use a Barlow).

I am also a little nervous about the nose of the Barlow hitting the prism in the diagonal.

Any thoughts would be really appreciated.

[Stu]

@Surfer Chris I would think a 4mm Delite would get a lot of use! A 7mm gives you x105 which is not high power! The 4mm at x185 would be very useable on reasonable nights, and the Delite has an excellent reputation. There is the Vixen HR 3.4mm which is excellent, up there with the very best, but at x217 is likely to be used less frequently. A barlowed 7mm Delite gives you x210 which again is less useable that the x185!

I use either a 3 to 6mm Nagler Zoom or a barlowed 8.9 to 17.8 Leica Zoom most frequently for mono high powered viewing, which allows you to tune the power to the conditions, giving x123 to x246. The eye relief is short but manageable at 10mm.

I’m not sure if you suffer from floaters at all, but I tend to Binoview for lunar and solar viewing these days as it does help reduce the visibility of these, plus gives a more relaxed view. I still use single eyepieces for doubles and a mix for planetary depending on how I’m feeling.

The main trouble is that you will end up needing a range of powers to cover the seeing conditions; x150, x180, x200, x220 ish are all useful, although the lower two will definitely be useable more often. That’s why people either build up a range of shorter focal length eyepieces, or opt for high quality Zooms like I have.

[Surfer Chris]

Thanks for the reply Stu.

Yeah I was thinking 185x would be a good magnification for my mount and scope.

I am kind of thinking that I might be better spending a little more money getting a 4mm and 7mm Delite (approx. £240 + 240) rather than the cost of a 7mm Delite + Barlow ( £240 + £120). Plus I am still unsure if I would run into issues with focus using the Barlow. Can always go back and ask the retailer about that though. I guess another plus with a Barlow is I could also use it with my Panoptic to get an effective 12mm?

Yes I have noticed some floaters with the 5mm BST EP when looking at the moon. I noticed a small cluster of 4 dots the other evening. Annoyingly they looked like very small craterlets. But thankfully not too distracting for me, so will hold off trying bino-viewing for a while yet (although I also said that I would wait a while before splashing out on more expensive eyepieces!!!).

The 3-6mm Nagler zoom was another option I was considering. I have read differing opinions though, some saying a fixed length EP such as the Delite will give slightly better views, and others saying that they see very little difference between the two? Plus of course the Delite has a wider FOV which may be beneficial with my manually driven Scopetech mount.

[Surfer Chris]

Something else I thought I would share with those using the Scopetech mount, I noticed when I first assembled the mount that the thread engagement between my Berlebach Report tripod and the Scopetech mount is very limited.

The threaded male stud on the Berlebach tripod is quite short at only 6.8mm high. And the corresponding female threaded hole on the Scopetech mount has a very big 3mm lead-in chamfer (see photo below).

This means that there is effectively only about 3mm of thread engagement between the two, and so only about 2 single turns of the thread holding my valuable scope and mount onto the tripod!!!! And to make things worse, the Scopetech mount is made from a fairly soft die-cast aluminium alloy, and the thread form is not great either (it looks like the tap drill used was slightly too big). So I have 2 turns of a thread in a soft aluminium alloy, and a poorly cut thread holding my Tak scope up! 

[Surfer Chris]

I am not too happy about this coupling. Generally, I will probably leave the mount always attached to the tripod. But if I was routinely dis-mantling the mount from the tripod, I would imagine the female thread would quite quickly wear or even fail through fatigue one day.

To reduce the risk, I am getting an engineering company to make up an adaptor plate I have drawn up. It will be a simple stainless steel disk (56.6mm OD x 7.5mm thick), with a 3/8" tapped hole running through the middle. I will then fix the adaptor plate to the 2x outboard M8 thread holes on the underside of the Scopetech mount using M8 countersunk screws. So the adaptor plate will become fixed to the mount. My Berlebach stud will then thread into the stronger stainless steel 3/8" thread on the adaptor plate. The threaded hole in the adaptor plate will not have the big 3mm lead-in chamfer, so it will provide more thread engagement with the stud.

[Surfer Chris]

I am sure those using the Scopetech and Berlebach combo may have already noticed this issue. But thought I would share it as a warning, especially for those routinely disassembling the mount from their tripods.

[Stu]

33 minutes ago, Surfer Chris said:

The 3-6mm Nagler zoom was another option I was considering. I have read differing opinions though, some saying a fixed length EP such as the Delite will give slightly better views, and others saying that they see very little difference between the two? Plus of course the Delite has a wider FOV which may be beneficial with my manually driven Scopetech mount.

Whilst the Nag zoom is excellent optically, I do think the Delite would have a slight edge over it. I’ve not do side by side comparisons, but I think the BGOs I have show the same edge.

[scotty38]

Removed post as wrong info....

Edited April 22, 2021 by scotty38

[Surfer Chris]

You made me doubt myself now. Just grabbed the Scopetech manual - and it is indicating the female thread is 3/8" like I said. But the thread form is not my main concern, it is the big 3mm chamfer on the lead-in to the female thread. That takes 3mm away from the possible thread engagement (which is already limited by the fact that the male stud is only 6.8mm high). It is the very limited (only 3mm) of thread engagement into a fairly soft alloy that concerns me. Thankfully I used to work for an engineering company, and they have offered to machine the adaptor plate for me.

[Cleetus]

2 hours ago, Surfer Chris said:

You made me doubt myself now. Just grabbed the Scopetech manual - and it is indicating the female thread is 3/8" like I said. But the thread form is not my main concern, it is the big 3mm chamfer on the lead-in to the female thread. That takes 3mm away from the possible thread engagement (which is already limited by the fact that the male stud is only 6.8mm high). It is the very limited (only 3mm) of thread engagement into a fairly soft alloy that concerns me. Thankfully I used to work for an engineering company, and they have offered to machine the adaptor plate for me.

Would it not be easier to swap out the screw in the tripod for a longer one?

[Surfer Chris]

That was my first hope (that I could simply get a longer screw).

I contacted Berlebach about it. They told me the screw height (6.8mm) is an international standard length and that is all they make as standard. Unfortunately the screw assembly (it includes a plastic over-moulded knob on the lower end) is captive within the tripod module insert (the screw is held captive by a plate I think that is bonded into the module). 

They mentioned about making me a special module with longer screw (the complete module is shown below). I didn't take the conversation any further though - as I suspect there will be a reasonable charge for Berlebach to make this custom module, and I am able to get my solution (the adaptor plate) made for free.

Just out of interest though, I might get back to Berlebach and ask them about the price for the custom module.

[Cleetus]

2 hours ago, Surfer Chris said:

That was my first hope (that I could simply get a longer screw).

I contacted Berlebach about it. They told me the screw height (6.8mm) is an international standard length and that is all they make as standard. Unfortunately the screw assembly (it includes a plastic over-moulded knob on the lower end) is captive within the tripod module insert (the screw is held captive by a plate I think that is bonded into the module). 

They mentioned about making me a special module with longer screw (the complete module is shown below). I didn't take the conversation any further though - as I suspect there will be a reasonable charge for Berlebach to make this custom module, and I am able to get my solution (the adaptor plate) made for free.

Just out of interest though, I might get back to Berlebach and ask them about the price for the custom module.

I have had dealings with them in the past and found them very helpful. Did you buy the tripod from them or from a UK dealer?

I remember a discussion on a forum a few years back, not SGL, and there were contributions from some very technical members. Your question has reminded me of it. Basically, it concerned the maximum strength a threaded screw would have depending on the number of turns imparted. I think the conclusion was that maximum strength was achieved after about two full turns. So, although it might seem suspect you probably have nothing to worry about. Having said that, if I was in your shoes I would be thinking the same thing. Peace of mind and all that.

Edited April 22, 2021 by Cleetus

[JeremyS]

1 hour ago, Cleetus said:

I have had dealings with them in the past and found them very helpful. Did you buy the tripod from them or from a UK dealer?

I remember a discussion on a forum a few years back, not SGL, and there were contributions from some very technical members. Your question has reminded me of it. Basically, it concerned the maximum strength a threaded screw would have depending on the number of turns imparted. I think the conclusion was that maximum strength was achieved after about two full turns. So, although it might seem suspect you probably have nothing to worry about. Having said that, if I was in your shoes I would be thinking the same thing. Peace of mind and all that.

Interesting. I’m sure our resident engineer @johninderby can comment on the number of turns required 

[johninderby]

Rule of thumb for thread engagement for full strength is minimum 1 times the diameter of the bolt in steel and 2x in aluminium.

Edited April 22, 2021 by johninderby

[Surfer Chris]

Purchased the tripod from UK dealer. To be fair Berlebach seem to be quite responsive to the e-mails I have sent so far. Have sent another e-mail to them this eve asking how much the module with custom screw will be.

I am a design engineer too (for my sins), and I also go by the rule of thumb of 1x thread diameter in steel and 2x in aluminium where I can. I believe that full strength can be developed over just two turns of a thread, but I know from experience that with aluminium threads, in cases where the thread is routinely assembled and disassembled, and where <1x thread diameter of engagement is used, eventually over many cycles (e.g. 100+) the thread will shear as the aluminium fails through fatigue.

[Tijl Verheyen]

Deez nuts

[HollyHound]

On 22/04/2021 at 12:39, Surfer Chris said:

Something else I thought I would share with those using the Scopetech mount, I noticed when I first assembled the mount that the thread engagement between my Berlebach Report tripod and the Scopetech mount is very limited.

The threaded male stud on the Berlebach tripod is quite short at only 6.8mm high. And the corresponding female threaded hole on the Scopetech mount has a very big 3mm lead-in chamfer (see photo below).

This means that there is effectively only about 3mm of thread engagement between the two, and so only about 2 single turns of the thread holding my valuable scope and mount onto the tripod!!!! And to make things worse, the Scopetech mount is made from a fairly soft die-cast aluminium alloy, and the thread form is not great either (it looks like the tap drill used was slightly too big). So I have 2 turns of a thread in a soft aluminium alloy, and a poorly cut thread holding my Tak scope up! 

Thank you so much for spotting this potential weakness... I've had my ScopeTech Zero mounted on a Berlebach Report 372, which is similar to the 312 etc, but has interchangeable heads. Mine has an EQ5/AZ5 head, which has an M10 bolt and the north alignment pin for those mounts (see photo). In order to use my ScopeTech, I got one of these adaptors...

https://www.firstlightoptics.com/skywatcher-star-adventurer/astro-essentials-3-8-photo-adapter-for-heq5-az5-tripod.html

However, this appears to suffer the same problem you've highlighted... whilst the connection of the adaptor to the tripod head is super solid, it's got the same short(er) 3/8 threaded bolt on top to engage with the ScopeTech 😬

I remembered seeing that ScopeTech have their own adaptors (which weren't available when I got mine) and they have one that fits the EQ5/AZ5 M10 head...

https://www.firstlightoptics.com/all-mounts-motors/scopetech_trip_adptr_v60.html

Now this one uses two bolts (M6 or M8 I'm not sure) to connect to the base of the ScopeTech and then that connects more solidly to the M10 bolt on the tripod mount head (there is no chamfer). So not only is the connection more secure, but there are two bolts not just one now, which has got to be better!

Anyway, I've ordered one from @FLO just now and will report back on how well it works. Of course, none of us hope ever to have to test the strength of these connections in the worst case, but I think I'd be more re-assured now.

I wonder whether you could just get the replacement EQ5/AZ5 M10 mount head insert from Berlebach for your Report and then use this ScopeTech adaptor 🤔

https://www.berlebach.de/en/?bereich=details&id=179

Thanks for the heads up and look forward to seeing your own engineering fix for this too.

Gary

Edited April 23, 2021 by HollyHound