# Lens setup focal length... equivalent or actual?

**URL:** https://forum.telescopius.com/t/lens-setup-focal-length-equivalent-or-actual/1802
**Category:** General Questions
**Created:** [May 16, 2025, 11:41pm UTC](https://forum.telescopius.com/t/lens-setup-focal-length-equivalent-or-actual/1802 "2025-05-16T23:41:47Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![jamesraykenney](https://forum.telescopius.com/user_avatar/forum.telescopius.com/jamesraykenney/32/896_2.png) [@jamesraykenney](https://forum.telescopius.com/u/jamesraykenney)
#### Post date: [May 16, 2025, 11:41pm UTC](https://forum.telescopius.com/t/lens-setup-focal-length-equivalent-or-actual/1802/1 "2025-05-16T23:41:47Z")

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When you add a lens under add telescope, it asks for the Focal length…  
Does it want the TRUE Focal length or the 35mm equivalent Focal length…  
For example…  
I have a Nikon P1100 with a 24mm to 3000mm equivalent Focal length but the actual Focal length is 4.2mm to 539mm  
I also have a Panasonic FZ2500 with a 24mm to 480mm equivalent Focal Length and an actual Focal length of 8.8mm to 176mm  
Which set of numbers do I use?

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### Author: ![sebagr](https://forum.telescopius.com/user_avatar/forum.telescopius.com/sebagr/32/6_2.png) [@sebagr](https://forum.telescopius.com/u/sebagr)
#### Post date: [May 19, 2025, 3:12pm UTC](https://forum.telescopius.com/t/lens-setup-focal-length-equivalent-or-actual/1802/2 "2025-05-19T15:12:17Z")

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Depending on the sensor size you enter, you can use both.

- You can enter a full frame sensor in the camera settings, in which case you need to use the equivalent focal length (easier)

- Or you can use the real sensor size (not full frame), in which case you’ll need to enter the actual focal length.

For framing purposes both approaches are equivalent.