diff --git a/src/ScaleAperture.jl b/src/ScaleAperture.jl
index 0cfb6ec..d7c5d1d 100644
--- a/src/ScaleAperture.jl
+++ b/src/ScaleAperture.jl
@@ -46,7 +46,7 @@ function J(v::Vector{Float64}, ε::Float64; precision = 3, finesse::Int = 101)
     Λ(ΔW, b, v2, n_max; finesse)
 end
 
-function J(v::Vector{Float64}, ε::Float64, ::Model; precision = 3)
+function J(v::Vector{Float64}, ε::Float64, ::Type{Model}; precision = 3)
     v2, n_max = Π(v, ε)
     Zᵢ = Vector{Polynomial}(undef, length(v))
     Ψ(v2, Zᵢ, n_max; precision)[1]
diff --git a/src/TransformAperture.jl b/src/TransformAperture.jl
index 8f741d3..6a3fc57 100644
--- a/src/TransformAperture.jl
+++ b/src/TransformAperture.jl
@@ -184,23 +184,23 @@ function P(v::Vector{T}, ε::T, δ::Complex{T} = 0.0im,
     Λ(ΔW, b, v2, n_max; finesse)
 end
 
-function P(v::Vector{T}, ε::T, δ::Complex{T}, ϕ::T, ω::Tuple{T, T}, ::Model;
+function P(v::Vector{T}, ε::T, δ::Complex{T}, ϕ::T, ω::Tuple{T, T}, ::Type{Model};
            precision = 3) where T <: Float64
     v2, n_max = S(v, ε, δ, ϕ, ω)
     Zᵢ = Vector{Polynomial}(undef, length(v))
     Ψ(v2, Zᵢ, n_max; precision)[1]
 end
 
-function P(v::Vector{T}, ε::T, ::Model; precision = 3) where T <: Float64
-    P(v, ε, 0.0im, zero(T), (1.0, 0.0), Model(); precision)
+function P(v::Vector{T}, ε::T, ::Type{Model}; precision = 3) where T <: Float64
+    P(v, ε, 0.0im, zero(T), (1.0, 0.0), Model; precision)
 end
 
-function P(v::Vector{T}, ε::T, δ::Complex{T}, ::Model;
+function P(v::Vector{T}, ε::T, δ::Complex{T}, ::Type{Model};
            precision = 3) where T <: Float64
-    P(v, ε, δ, zero(T), (1.0, 0.0), Model(); precision)
+    P(v, ε, δ, zero(T), (1.0, 0.0), Model; precision)
 end
 
-function P(v::Vector{T}, ε::T, δ::Complex{T}, ϕ::T, ::Model;
+function P(v::Vector{T}, ε::T, δ::Complex{T}, ϕ::T, ::Type{Model};
            precision = 3) where T <: Float64
-    P(v, ε, δ, ϕ, (1.0, 0.0), Model(); precision)
+    P(v, ε, δ, ϕ, (1.0, 0.0), Model; precision)
 end
diff --git a/src/WavefrontError.jl b/src/WavefrontError.jl
index f33493f..0a4ce3a 100644
--- a/src/WavefrontError.jl
+++ b/src/WavefrontError.jl
@@ -31,7 +31,7 @@ end
 # fitting function (construction function 1)
 function Wf(ρ::FloatVec, θ::FloatVec, OPD::FloatVec, n_max::Int)
     j_max = get_j(n_max, n_max)
-    Zᵢ = Polynomial[Z(j, Model()) for j = 0:j_max]
+    Zᵢ = Polynomial[Z(j, Model) for j = 0:j_max]
     v = fit(ρ, θ, OPD, Zᵢ)
     return v, Zᵢ
 end
@@ -57,7 +57,7 @@ function Ψ(v, Zᵢ, n_max, orders = Tuple{Int, Int}[]; precision)
         aᵢ = precision == "full" ? aᵢ : round(aᵢ; digits = precision)
         if !iszero(aᵢ)
             if clipped
-                Zᵢ[i] = Z(i-1, Model())
+                Zᵢ[i] = Z(i-1, Model)
             end
             push!(a, (; Zᵢ[i].inds..., a = aᵢ))
             push!(av, aᵢ)
@@ -147,14 +147,14 @@ function standardize(v_sub::FloatVec, orders::Vector{Tuple{Int, Int}})
 end
 
 # methods
-function W(ρ::FloatVec, θ::FloatVec, OPD::FloatVec, n_max::Int, ::Model;
+function W(ρ::FloatVec, θ::FloatVec, OPD::FloatVec, n_max::Int, ::Type{Model};
            precision = 3)
     v, Zᵢ = Wf(ρ, θ, OPD, n_max)
     return Ψ(v, Zᵢ, n_max; precision)[1]
 end
 
 function W(ρ::FloatVec, θ::FloatVec, OPD::FloatVec,
-           orders::Vector{Tuple{Int, Int}}, ::Model; precision = 3)
+           orders::Vector{Tuple{Int, Int}}, ::Type{Model}; precision = 3)
     n_max = maximum(mn -> mn[2], orders; init = 0)
     v, Zᵢ = Wf(ρ, θ, OPD, orders)
     return Ψ(v, Zᵢ, n_max, orders; precision)[1]
@@ -186,8 +186,8 @@ function W(OPD::FloatMat, fit_to; options...)
     W(coords(OPD)..., vec(OPD), fit_to; options...)
 end
 
-function W(OPD::FloatMat, fit_to, ::Model; precision = 3)
-    W(coords(OPD)..., vec(OPD), fit_to, Model(); precision)
+function W(OPD::FloatMat, fit_to, ::Type{Model}; precision = 3)
+    W(coords(OPD)..., vec(OPD), fit_to, Model; precision)
 end
 
 # reverse transform;
diff --git a/src/Zernike.jl b/src/Zernike.jl
index 299762a..9af505c 100644
--- a/src/Zernike.jl
+++ b/src/Zernike.jl
@@ -239,12 +239,12 @@ getindex(Z::T, i) where {T <: Output} = getfield(Z, fieldnames(T)[i])
 iterate(Z::Output, i = 1) = (i > 3 ? nothing : (Z[i], i + 1))
 
 # methods
-Z(m::Int, n::Int, ::Model) = Zf(m, n)
+Z(m::Int, n::Int, ::Type{Model}) = Zf(m, n)
 
 Z(; m, n, finesse::Int = 100) = Z(m, n; finesse)
 
 Z(j::Int; finesse::Int = 100) = Z(get_mn(j)...; finesse)
 
-Z(j::Int, ::Model) = Zf(get_mn(j)...)
+Z(j::Int, ::Type{Model}) = Zf(get_mn(j)...)
 
 end